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authorakiyamn2023-09-24 23:22:21 +1000
committerakiyamn2023-09-24 23:22:21 +1000
commit4e87195739f2a5d9a05451b48773c8afdc680765 (patch)
tree9cba501844a4a11dcbdffc4050ed8189561c55ed /node_modules/capnp-ts/src/serialization/pointers/pointer.ts
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+/**
+ * @author jdiaz5513
+ */
+
+import initTrace from "debug";
+
+import { LIST_SIZE_MASK, MAX_DEPTH, POINTER_DOUBLE_FAR_MASK, POINTER_TYPE_MASK } from "../../constants";
+import { bufferToHex, format, padToWord } from "../../util";
+import { ListElementSize } from "../list-element-size";
+import {
+ ObjectSize,
+ getByteLength,
+ padToWord as padObjectToWord,
+ getWordLength,
+ getDataWordLength,
+} from "../object-size";
+import { Segment } from "../segment";
+import { Orphan } from "./orphan";
+import { PointerAllocationResult } from "./pointer-allocation-result";
+import { PointerType } from "./pointer-type";
+import { Message } from "../message";
+import {
+ PTR_TRAVERSAL_LIMIT_EXCEEDED,
+ PTR_DEPTH_LIMIT_EXCEEDED,
+ PTR_OFFSET_OUT_OF_BOUNDS,
+ PTR_INVALID_LIST_SIZE,
+ PTR_INVALID_POINTER_TYPE,
+ PTR_INVALID_FAR_TARGET,
+ TYPE_COMPOSITE_SIZE_UNDEFINED,
+ PTR_WRONG_POINTER_TYPE,
+ PTR_WRONG_LIST_TYPE,
+ INVARIANT_UNREACHABLE_CODE,
+} from "../../errors";
+
+const trace = initTrace("capnp:pointer");
+trace("load");
+
+export interface _PointerCtor {
+ readonly displayName: string;
+}
+
+export interface PointerCtor<T extends Pointer> {
+ readonly _capnp: _PointerCtor;
+
+ new (segment: Segment, byteOffset: number, depthLimit?: number): T;
+}
+
+export interface _Pointer {
+ compositeIndex?: number;
+
+ compositeList: boolean;
+
+ /**
+ * A number that is decremented as nested pointers are traversed. When this hits zero errors will be thrown.
+ */
+
+ depthLimit: number;
+}
+
+/**
+ * A pointer referencing a single byte location in a segment. This is typically used for Cap'n Proto pointers, but is
+ * also sometimes used to reference an offset to a pointer's content or tag words.
+ *
+ * @export
+ * @class Pointer
+ */
+
+export class Pointer {
+ static readonly adopt = adopt;
+ static readonly copyFrom = copyFrom;
+ static readonly disown = disown;
+ static readonly dump = dump;
+ static readonly isNull = isNull;
+
+ static readonly _capnp: _PointerCtor = {
+ displayName: "Pointer" as string,
+ };
+
+ readonly _capnp: _Pointer;
+
+ /** Offset, in bytes, from the start of the segment to the beginning of this pointer. */
+
+ byteOffset: number;
+
+ /**
+ * The starting segment for this pointer's data. In the case of a far pointer, the actual content this pointer is
+ * referencing will be in another segment within the same message.
+ */
+
+ segment: Segment;
+
+ constructor(segment: Segment, byteOffset: number, depthLimit = MAX_DEPTH) {
+ this._capnp = { compositeList: false, depthLimit };
+ this.segment = segment;
+ this.byteOffset = byteOffset;
+
+ if (depthLimit === 0) {
+ throw new Error(format(PTR_DEPTH_LIMIT_EXCEEDED, this));
+ }
+
+ // Make sure we keep track of all pointer allocations; there's a limit per message (prevent DoS).
+
+ trackPointerAllocation(segment.message, this);
+
+ // NOTE: It's okay to have a pointer to the end of the segment; you'll see this when creating pointers to the
+ // beginning of the content of a newly-allocated composite list with zero elements. Unlike other language
+ // implementations buffer over/underflows are not a big issue since all buffer access is bounds checked in native
+ // code anyway.
+
+ if (byteOffset < 0 || byteOffset > segment.byteLength) {
+ throw new Error(format(PTR_OFFSET_OUT_OF_BOUNDS, byteOffset));
+ }
+
+ trace("new %s", this);
+ }
+
+ toString(): string {
+ return format("Pointer_%d@%a,%s,limit:%x", this.segment.id, this.byteOffset, dump(this), this._capnp.depthLimit);
+ }
+}
+
+/**
+ * Adopt an orphaned pointer, making the pointer point to the orphaned content without copying it.
+ *
+ * @param {Orphan<Pointer>} src The orphan to adopt.
+ * @param {Pointer} p The the pointer to adopt into.
+ * @returns {void}
+ */
+
+export function adopt<T extends Pointer>(src: Orphan<T>, p: T): void {
+ src._moveTo(p);
+}
+
+/**
+ * Convert a pointer to an Orphan, zeroing out the pointer and leaving its content untouched. If the content is no
+ * longer needed, call `disown()` on the orphaned pointer to erase the contents as well.
+ *
+ * Call `adopt()` on the orphan with the new target pointer location to move it back into the message; the orphan
+ * object is then invalidated after adoption (can only adopt once!).
+ *
+ * @param {T} p The pointer to turn into an Orphan.
+ * @returns {Orphan<T>} An orphaned pointer.
+ */
+
+export function disown<T extends Pointer>(p: T): Orphan<T> {
+ return new Orphan(p);
+}
+
+export function dump(p: Pointer): string {
+ return bufferToHex(p.segment.buffer.slice(p.byteOffset, p.byteOffset + 8));
+}
+
+/**
+ * Get the total number of bytes required to hold a list of the provided size with the given length, rounded up to the
+ * nearest word.
+ *
+ * @param {ListElementSize} elementSize A number describing the size of the list elements.
+ * @param {number} length The length of the list.
+ * @param {ObjectSize} [compositeSize] The size of each element in a composite list; required if
+ * `elementSize === ListElementSize.COMPOSITE`.
+ * @returns {number} The number of bytes required to hold an element of that size, or `NaN` if that is undefined.
+ */
+
+export function getListByteLength(elementSize: ListElementSize, length: number, compositeSize?: ObjectSize): number {
+ switch (elementSize) {
+ case ListElementSize.BIT:
+ return padToWord((length + 7) >>> 3);
+
+ case ListElementSize.BYTE:
+ case ListElementSize.BYTE_2:
+ case ListElementSize.BYTE_4:
+ case ListElementSize.BYTE_8:
+ case ListElementSize.POINTER:
+ case ListElementSize.VOID:
+ return padToWord(getListElementByteLength(elementSize) * length);
+
+ /* istanbul ignore next */
+ case ListElementSize.COMPOSITE:
+ if (compositeSize === undefined) {
+ throw new Error(format(PTR_INVALID_LIST_SIZE, NaN));
+ }
+
+ return length * padToWord(getByteLength(compositeSize));
+
+ /* istanbul ignore next */
+ default:
+ throw new Error(PTR_INVALID_LIST_SIZE);
+ }
+}
+
+/**
+ * Get the number of bytes required to hold a list element of the provided size. `COMPOSITE` elements do not have a
+ * fixed size, and `BIT` elements are packed into exactly a single bit, so these both return `NaN`.
+ *
+ * @param {ListElementSize} elementSize A number describing the size of the list elements.
+ * @returns {number} The number of bytes required to hold an element of that size, or `NaN` if that is undefined.
+ */
+
+export function getListElementByteLength(elementSize: ListElementSize): number {
+ switch (elementSize) {
+ /* istanbul ignore next */
+ case ListElementSize.BIT:
+ return NaN;
+
+ case ListElementSize.BYTE:
+ return 1;
+
+ case ListElementSize.BYTE_2:
+ return 2;
+
+ case ListElementSize.BYTE_4:
+ return 4;
+
+ case ListElementSize.BYTE_8:
+ case ListElementSize.POINTER:
+ return 8;
+
+ /* istanbul ignore next */
+ case ListElementSize.COMPOSITE:
+ // Caller has to figure it out based on the tag word.
+
+ return NaN;
+
+ /* istanbul ignore next */
+ case ListElementSize.VOID:
+ return 0;
+
+ /* istanbul ignore next */
+ default:
+ throw new Error(format(PTR_INVALID_LIST_SIZE, elementSize));
+ }
+}
+
+/**
+ * Add an offset to the pointer's offset and return a new Pointer for that address.
+ *
+ * @param {number} offset The number of bytes to add to the offset.
+ * @param {Pointer} p The pointer to add from.
+ * @returns {Pointer} A new pointer to the address.
+ */
+
+export function add(offset: number, p: Pointer): Pointer {
+ return new Pointer(p.segment, p.byteOffset + offset, p._capnp.depthLimit);
+}
+
+/**
+ * Replace a pointer with a deep copy of the pointer at `src` and all of its contents.
+ *
+ * @param {Pointer} src The pointer to copy.
+ * @param {Pointer} p The pointer to copy into.
+ * @returns {void}
+ */
+
+export function copyFrom(src: Pointer, p: Pointer): void {
+ // If the pointer is the same then this is a noop.
+
+ if (p.segment === src.segment && p.byteOffset === src.byteOffset) {
+ trace("ignoring copy operation from identical pointer %s", src);
+
+ return;
+ }
+
+ // Make sure we erase this pointer's contents before moving on. If src is null, that's all we do.
+
+ erase(p); // noop if null
+
+ if (isNull(src)) return;
+
+ switch (getTargetPointerType(src)) {
+ case PointerType.STRUCT:
+ copyFromStruct(src, p);
+
+ break;
+
+ case PointerType.LIST:
+ copyFromList(src, p);
+
+ break;
+
+ /* istanbul ignore next */
+ default:
+ throw new Error(format(PTR_INVALID_POINTER_TYPE, getTargetPointerType(p)));
+ }
+}
+
+/**
+ * Recursively erase a pointer, any far pointers/landing pads/tag words, and the content it points to.
+ *
+ * Note that this will leave "holes" of zeroes in the message, since the space cannot be reclaimed. With packing this
+ * will have a negligible effect on the final message size.
+ *
+ * FIXME: This may need protection against infinite recursion...
+ *
+ * @param {Pointer} p The pointer to erase.
+ * @returns {void}
+ */
+
+export function erase(p: Pointer): void {
+ if (isNull(p)) return;
+
+ // First deal with the contents.
+
+ let c: Pointer;
+
+ switch (getTargetPointerType(p)) {
+ case PointerType.STRUCT: {
+ const size = getTargetStructSize(p);
+ c = getContent(p);
+
+ // Wipe the data section.
+
+ c.segment.fillZeroWords(c.byteOffset, size.dataByteLength / 8);
+
+ // Iterate over all the pointers and nuke them.
+
+ for (let i = 0; i < size.pointerLength; i++) {
+ erase(add(i * 8, c));
+ }
+
+ break;
+ }
+ case PointerType.LIST: {
+ const elementSize = getTargetListElementSize(p);
+ const length = getTargetListLength(p);
+ let contentWords = padToWord(length * getListElementByteLength(elementSize));
+ c = getContent(p);
+
+ if (elementSize === ListElementSize.POINTER) {
+ for (let i = 0; i < length; i++) {
+ erase(new Pointer(c.segment, c.byteOffset + i * 8, p._capnp.depthLimit - 1));
+ }
+
+ // Calling erase on each pointer takes care of the content, nothing left to do here.
+
+ break;
+ } else if (elementSize === ListElementSize.COMPOSITE) {
+ // Read some stuff from the tag word.
+ const tag = add(-8, c);
+ const compositeSize = getStructSize(tag);
+ const compositeByteLength = getByteLength(compositeSize);
+ contentWords = getOffsetWords(tag);
+
+ // Kill the tag word.
+ c.segment.setWordZero(c.byteOffset - 8);
+
+ // Recursively erase each pointer.
+ for (let i = 0; i < length; i++) {
+ for (let j = 0; j < compositeSize.pointerLength; j++) {
+ erase(new Pointer(c.segment, c.byteOffset + i * compositeByteLength + j * 8, p._capnp.depthLimit - 1));
+ }
+ }
+ }
+
+ c.segment.fillZeroWords(c.byteOffset, contentWords);
+
+ break;
+ }
+ case PointerType.OTHER:
+ // No content.
+
+ break;
+
+ default:
+ throw new Error(format(PTR_INVALID_POINTER_TYPE, getTargetPointerType(p)));
+ }
+
+ erasePointer(p);
+}
+
+/**
+ * Set the pointer (and far pointer landing pads, if applicable) to zero. Does not touch the pointer's content.
+ *
+ * @param {Pointer} p The pointer to erase.
+ * @returns {void}
+ */
+
+export function erasePointer(p: Pointer): void {
+ if (getPointerType(p) === PointerType.FAR) {
+ const landingPad = followFar(p);
+
+ if (isDoubleFar(p)) {
+ // Kill the double-far tag word.
+
+ landingPad.segment.setWordZero(landingPad.byteOffset + 8);
+ }
+
+ // Kill the landing pad.
+
+ landingPad.segment.setWordZero(landingPad.byteOffset);
+ }
+
+ // Finally! Kill the pointer itself...
+
+ p.segment.setWordZero(p.byteOffset);
+}
+
+/**
+ * Interpret the pointer as a far pointer, returning its target segment and offset.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {Pointer} A pointer to the far target.
+ */
+
+export function followFar(p: Pointer): Pointer {
+ const targetSegment = p.segment.message.getSegment(p.segment.getUint32(p.byteOffset + 4));
+ const targetWordOffset = p.segment.getUint32(p.byteOffset) >>> 3;
+
+ return new Pointer(targetSegment, targetWordOffset * 8, p._capnp.depthLimit - 1);
+}
+
+/**
+ * If the pointer address references a far pointer, follow it to the location where the actual pointer data is written.
+ * Otherwise, returns the pointer unmodified.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {Pointer} A new pointer representing the target location, or `p` if it is not a far pointer.
+ */
+
+export function followFars(p: Pointer): Pointer {
+ if (getPointerType(p) === PointerType.FAR) {
+ const landingPad = followFar(p);
+
+ if (isDoubleFar(p)) landingPad.byteOffset += 8;
+
+ return landingPad;
+ }
+
+ return p;
+}
+
+export function getCapabilityId(p: Pointer): number {
+ return p.segment.getUint32(p.byteOffset + 4);
+}
+
+function isCompositeList(p: Pointer): boolean {
+ return getTargetPointerType(p) === PointerType.LIST && getTargetListElementSize(p) === ListElementSize.COMPOSITE;
+}
+
+/**
+ * Obtain the location of the pointer's content, following far pointers as needed.
+ * If the pointer is a struct pointer and `compositeIndex` is set, it will be offset by a multiple of the struct's size.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @param {boolean} [ignoreCompositeIndex] If true, will not follow the composite struct pointer's composite index and
+ * instead return a pointer to the parent list's contents (also the beginning of the first struct).
+ * @returns {Pointer} A pointer to the beginning of the pointer's content.
+ */
+
+export function getContent(p: Pointer, ignoreCompositeIndex?: boolean): Pointer {
+ let c: Pointer;
+
+ if (isDoubleFar(p)) {
+ const landingPad = followFar(p);
+ c = new Pointer(p.segment.message.getSegment(getFarSegmentId(landingPad)), getOffsetWords(landingPad) * 8);
+ } else {
+ const target = followFars(p);
+ c = new Pointer(target.segment, target.byteOffset + 8 + getOffsetWords(target) * 8);
+ }
+
+ if (isCompositeList(p)) c.byteOffset += 8;
+
+ if (!ignoreCompositeIndex && p._capnp.compositeIndex !== undefined) {
+ // Seek backwards by one word so we can read the struct size off the tag word.
+
+ c.byteOffset -= 8;
+
+ // Seek ahead by `compositeIndex` multiples of the struct's total size.
+
+ c.byteOffset += 8 + p._capnp.compositeIndex * getByteLength(padObjectToWord(getStructSize(c)));
+ }
+
+ return c;
+}
+
+/**
+ * Read the target segment ID from a far pointer.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {number} The target segment ID.
+ */
+
+export function getFarSegmentId(p: Pointer): number {
+ return p.segment.getUint32(p.byteOffset + 4);
+}
+
+/**
+ * Get a number indicating the size of the list's elements.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {ListElementSize} The size of the list's elements.
+ */
+
+export function getListElementSize(p: Pointer): ListElementSize {
+ return p.segment.getUint32(p.byteOffset + 4) & LIST_SIZE_MASK;
+}
+
+/**
+ * Get the number of elements in a list pointer. For composite lists, it instead represents the total number of words in
+ * the list (not counting the tag word).
+ *
+ * This method does **not** attempt to distinguish between composite and non-composite lists. To get the correct
+ * length for composite lists use `getTargetListLength()` instead.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {number} The length of the list, or total number of words for composite lists.
+ */
+
+export function getListLength(p: Pointer): number {
+ return p.segment.getUint32(p.byteOffset + 4) >>> 3;
+}
+
+/**
+ * Get the offset (in words) from the end of a pointer to the start of its content. For struct pointers, this is the
+ * beginning of the data section, and for list pointers it is the location of the first element. The value should
+ * always be zero for interface pointers.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {number} The offset, in words, from the end of the pointer to the start of the data section.
+ */
+
+export function getOffsetWords(p: Pointer): number {
+ const o = p.segment.getInt32(p.byteOffset);
+
+ // Far pointers only have 29 offset bits.
+ return o & 2 ? o >> 3 : o >> 2;
+}
+
+/**
+ * Look up the pointer's type.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {PointerType} The type of pointer.
+ */
+
+export function getPointerType(p: Pointer): PointerType {
+ return p.segment.getUint32(p.byteOffset) & POINTER_TYPE_MASK;
+}
+
+/**
+ * Read the number of data words from this struct pointer.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {number} The number of data words in the struct.
+ */
+
+export function getStructDataWords(p: Pointer): number {
+ return p.segment.getUint16(p.byteOffset + 4);
+}
+
+/**
+ * Read the number of pointers contained in this struct pointer.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {number} The number of pointers in this struct.
+ */
+
+export function getStructPointerLength(p: Pointer): number {
+ return p.segment.getUint16(p.byteOffset + 6);
+}
+
+/**
+ * Get an object describing this struct pointer's size.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {ObjectSize} The size of the struct.
+ */
+
+export function getStructSize(p: Pointer): ObjectSize {
+ return new ObjectSize(getStructDataWords(p) * 8, getStructPointerLength(p));
+}
+
+/**
+ * Get a pointer to this pointer's composite list tag word, following far pointers as needed.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {Pointer} A pointer to the list's composite tag word.
+ */
+
+export function getTargetCompositeListTag(p: Pointer): Pointer {
+ const c = getContent(p);
+
+ // The composite list tag is always one word before the content.
+
+ c.byteOffset -= 8;
+
+ return c;
+}
+
+/**
+ * Get the object size for the target composite list, following far pointers as needed.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {ObjectSize} An object describing the size of each struct in the list.
+ */
+
+export function getTargetCompositeListSize(p: Pointer): ObjectSize {
+ return getStructSize(getTargetCompositeListTag(p));
+}
+
+/**
+ * Get the size of the list elements referenced by this pointer, following far pointers if necessary.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {ListElementSize} The size of the elements in the list.
+ */
+
+export function getTargetListElementSize(p: Pointer): ListElementSize {
+ return getListElementSize(followFars(p));
+}
+
+/**
+ * Get the length of the list referenced by this pointer, following far pointers if necessary. If the list is a
+ * composite list, it will look up the tag word and read the length from there.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {number} The number of elements in the list.
+ */
+
+export function getTargetListLength(p: Pointer): number {
+ const t = followFars(p);
+
+ if (getListElementSize(t) === ListElementSize.COMPOSITE) {
+ // The content is prefixed by a tag word; it's a struct pointer whose offset contains the list's length.
+
+ return getOffsetWords(getTargetCompositeListTag(p));
+ }
+
+ return getListLength(t);
+}
+
+/**
+ * Get the type of a pointer, following far pointers if necessary. For non-far pointers this is equivalent to calling
+ * `getPointerType()`.
+ *
+ * The target of a far pointer can never be another far pointer, and this method will throw if such a situation is
+ * encountered.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {PointerType} The type of pointer referenced by this pointer.
+ */
+
+export function getTargetPointerType(p: Pointer): PointerType {
+ const t = getPointerType(followFars(p));
+
+ if (t === PointerType.FAR) throw new Error(format(PTR_INVALID_FAR_TARGET, p));
+
+ return t;
+}
+
+/**
+ * Get the size of the struct referenced by a pointer, following far pointers if necessary.
+ *
+ * @param {Pointer} p The poiner to read from.
+ * @returns {ObjectSize} The size of the struct referenced by this pointer.
+ */
+
+export function getTargetStructSize(p: Pointer): ObjectSize {
+ return getStructSize(followFars(p));
+}
+
+/**
+ * Initialize a pointer to point at the data in the content segment. If the content segment is not the same as the
+ * pointer's segment, this will allocate and write far pointers as needed. Nothing is written otherwise.
+ *
+ * The return value includes a pointer to write the pointer's actual data to (the eventual far target), and the offset
+ * value (in words) to use for that pointer. In the case of double-far pointers this offset will always be zero.
+ *
+ * @param {Segment} contentSegment The segment containing this pointer's content.
+ * @param {number} contentOffset The offset within the content segment for the beginning of this pointer's content.
+ * @param {Pointer} p The pointer to initialize.
+ * @returns {PointerAllocationResult} An object containing a pointer (where the pointer data should be written), and
+ * the value to use as the offset for that pointer.
+ */
+
+export function initPointer(contentSegment: Segment, contentOffset: number, p: Pointer): PointerAllocationResult {
+ if (p.segment !== contentSegment) {
+ // Need a far pointer.
+
+ trace("Initializing far pointer %s -> %s.", p, contentSegment);
+
+ if (!contentSegment.hasCapacity(8)) {
+ // GAH! Not enough space in the content segment for a landing pad so we need a double far pointer.
+
+ const landingPad = p.segment.allocate(16);
+
+ trace("GAH! Initializing double-far pointer in %s from %s -> %s.", p, contentSegment, landingPad);
+
+ setFarPointer(true, landingPad.byteOffset / 8, landingPad.segment.id, p);
+ setFarPointer(false, contentOffset / 8, contentSegment.id, landingPad);
+
+ landingPad.byteOffset += 8;
+
+ return new PointerAllocationResult(landingPad, 0);
+ }
+
+ // Allocate a far pointer landing pad in the target segment.
+
+ const landingPad = contentSegment.allocate(8);
+
+ if (landingPad.segment.id !== contentSegment.id) {
+ throw new Error(INVARIANT_UNREACHABLE_CODE);
+ }
+
+ setFarPointer(false, landingPad.byteOffset / 8, landingPad.segment.id, p);
+
+ return new PointerAllocationResult(landingPad, (contentOffset - landingPad.byteOffset - 8) / 8);
+ }
+
+ trace("Initializing intra-segment pointer %s -> %a.", p, contentOffset);
+
+ return new PointerAllocationResult(p, (contentOffset - p.byteOffset - 8) / 8);
+}
+
+/**
+ * Check if the pointer is a double-far pointer.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {boolean} `true` if it is a double-far pointer, `false` otherwise.
+ */
+
+export function isDoubleFar(p: Pointer): boolean {
+ return getPointerType(p) === PointerType.FAR && (p.segment.getUint32(p.byteOffset) & POINTER_DOUBLE_FAR_MASK) !== 0;
+}
+
+/**
+ * Quickly check to see if the pointer is "null". A "null" pointer is a zero word, equivalent to an empty struct
+ * pointer.
+ *
+ * @param {Pointer} p The pointer to read from.
+ * @returns {boolean} `true` if the pointer is "null".
+ */
+
+export function isNull(p: Pointer): boolean {
+ return p.segment.isWordZero(p.byteOffset);
+}
+
+/**
+ * Relocate a pointer to the given destination, ensuring that it points to the same content. This will create far
+ * pointers as needed if the content is in a different segment than the destination. After the relocation the source
+ * pointer will be erased and is no longer valid.
+ *
+ * @param {Pointer} dst The desired location for the `src` pointer. Any existing contents will be erased before
+ * relocating!
+ * @param {Pointer} src The pointer to relocate.
+ * @returns {void}
+ */
+
+export function relocateTo(dst: Pointer, src: Pointer): void {
+ const t = followFars(src);
+ const lo = t.segment.getUint8(t.byteOffset) & 0x03; // discard the offset
+ const hi = t.segment.getUint32(t.byteOffset + 4);
+
+ // Make sure anything dst was pointing to is wiped out.
+ erase(dst);
+
+ const res = initPointer(t.segment, t.byteOffset + 8 + getOffsetWords(t) * 8, dst);
+
+ // Keep the low 2 bits and write the new offset.
+ res.pointer.segment.setUint32(res.pointer.byteOffset, lo | (res.offsetWords << 2));
+ // Keep the high 32 bits intact.
+ res.pointer.segment.setUint32(res.pointer.byteOffset + 4, hi);
+
+ erasePointer(src);
+}
+
+/**
+ * Write a far pointer.
+ *
+ * @param {boolean} doubleFar Set to `true` if this is a double far pointer.
+ * @param {number} offsetWords The offset, in words, to the target pointer.
+ * @param {number} segmentId The segment the target pointer is located in.
+ * @param {Pointer} p The pointer to write to.
+ * @returns {void}
+ */
+
+export function setFarPointer(doubleFar: boolean, offsetWords: number, segmentId: number, p: Pointer): void {
+ const A = PointerType.FAR;
+ const B = doubleFar ? 1 : 0;
+ const C = offsetWords;
+ const D = segmentId;
+
+ p.segment.setUint32(p.byteOffset, A | (B << 2) | (C << 3));
+ p.segment.setUint32(p.byteOffset + 4, D);
+}
+
+/**
+ * Write a raw interface pointer.
+ *
+ * @param {number} capId The capability ID.
+ * @param {Pointer} p The pointer to write to.
+ * @returns {void}
+ */
+
+export function setInterfacePointer(capId: number, p: Pointer): void {
+ p.segment.setUint32(p.byteOffset, PointerType.OTHER);
+ p.segment.setUint32(p.byteOffset + 4, capId);
+}
+
+/**
+ * Write a raw list pointer.
+ *
+ * @param {number} offsetWords The number of words from the end of this pointer to the beginning of the list content.
+ * @param {ListElementSize} size The size of each element in the list.
+ * @param {number} length The number of elements in the list.
+ * @param {Pointer} p The pointer to write to.
+ * @param {ObjectSize} [compositeSize] For composite lists this describes the size of each element in this list. This
+ * is required for composite lists.
+ * @returns {void}
+ */
+
+export function setListPointer(
+ offsetWords: number,
+ size: ListElementSize,
+ length: number,
+ p: Pointer,
+ compositeSize?: ObjectSize
+): void {
+ const A = PointerType.LIST;
+ const B = offsetWords;
+ const C = size;
+ let D = length;
+
+ if (size === ListElementSize.COMPOSITE) {
+ if (compositeSize === undefined) {
+ throw new TypeError(TYPE_COMPOSITE_SIZE_UNDEFINED);
+ }
+
+ D *= getWordLength(compositeSize);
+ }
+
+ p.segment.setUint32(p.byteOffset, A | (B << 2));
+ p.segment.setUint32(p.byteOffset + 4, C | (D << 3));
+}
+
+/**
+ * Write a raw struct pointer.
+ *
+ * @param {number} offsetWords The number of words from the end of this pointer to the beginning of the struct's data
+ * section.
+ * @param {ObjectSize} size An object describing the size of the struct.
+ * @param {Pointer} p The pointer to write to.
+ * @returns {void}
+ */
+
+export function setStructPointer(offsetWords: number, size: ObjectSize, p: Pointer): void {
+ const A = PointerType.STRUCT;
+ const B = offsetWords;
+ const C = getDataWordLength(size);
+ const D = size.pointerLength;
+
+ p.segment.setUint32(p.byteOffset, A | (B << 2));
+ p.segment.setUint16(p.byteOffset + 4, C);
+ p.segment.setUint16(p.byteOffset + 6, D);
+}
+
+/**
+ * Read some bits off a pointer to make sure it has the right pointer data.
+ *
+ * @param {PointerType} pointerType The expected pointer type.
+ * @param {Pointer} p The pointer to validate.
+ * @param {ListElementSize} [elementSize] For list pointers, the expected element size. Leave this
+ * undefined for struct pointers.
+ * @returns {void}
+ */
+
+export function validate(pointerType: PointerType, p: Pointer, elementSize?: ListElementSize): void {
+ if (isNull(p)) return;
+
+ const t = followFars(p);
+
+ // Check the pointer type.
+
+ const A = t.segment.getUint32(t.byteOffset) & POINTER_TYPE_MASK;
+
+ if (A !== pointerType) {
+ throw new Error(format(PTR_WRONG_POINTER_TYPE, p, pointerType));
+ }
+
+ // Check the list element size, if provided.
+
+ if (elementSize !== undefined) {
+ const C = t.segment.getUint32(t.byteOffset + 4) & LIST_SIZE_MASK;
+
+ if (C !== elementSize) {
+ throw new Error(format(PTR_WRONG_LIST_TYPE, p, ListElementSize[elementSize]));
+ }
+ }
+}
+
+export function copyFromList(src: Pointer, dst: Pointer): void {
+ if (dst._capnp.depthLimit <= 0) throw new Error(PTR_DEPTH_LIMIT_EXCEEDED);
+
+ const srcContent = getContent(src);
+ const srcElementSize = getTargetListElementSize(src);
+ const srcLength = getTargetListLength(src);
+ let srcCompositeSize;
+ let srcStructByteLength;
+ let dstContent;
+
+ if (srcElementSize === ListElementSize.POINTER) {
+ dstContent = dst.segment.allocate(srcLength << 3);
+
+ // Recursively copy each pointer in the list.
+
+ for (let i = 0; i < srcLength; i++) {
+ const srcPtr = new Pointer(srcContent.segment, srcContent.byteOffset + (i << 3), src._capnp.depthLimit - 1);
+ const dstPtr = new Pointer(dstContent.segment, dstContent.byteOffset + (i << 3), dst._capnp.depthLimit - 1);
+
+ copyFrom(srcPtr, dstPtr);
+ }
+ } else if (srcElementSize === ListElementSize.COMPOSITE) {
+ srcCompositeSize = padObjectToWord(getTargetCompositeListSize(src));
+ srcStructByteLength = getByteLength(srcCompositeSize);
+
+ dstContent = dst.segment.allocate(getByteLength(srcCompositeSize) * srcLength + 8);
+
+ // Copy the tag word.
+
+ dstContent.segment.copyWord(dstContent.byteOffset, srcContent.segment, srcContent.byteOffset - 8);
+
+ // Copy the entire contents, including all pointers. This should be more efficient than making `srcLength`
+ // copies to skip the pointer sections, and we're about to rewrite all those pointers anyway.
+
+ // PERF: Skip this step if the composite struct only contains pointers.
+ if (srcCompositeSize.dataByteLength > 0) {
+ const wordLength = getWordLength(srcCompositeSize) * srcLength;
+
+ dstContent.segment.copyWords(dstContent.byteOffset + 8, srcContent.segment, srcContent.byteOffset, wordLength);
+ }
+
+ // Recursively copy all the pointers in each struct.
+
+ for (let i = 0; i < srcLength; i++) {
+ for (let j = 0; j < srcCompositeSize.pointerLength; j++) {
+ const offset = i * srcStructByteLength + srcCompositeSize.dataByteLength + (j << 3);
+
+ const srcPtr = new Pointer(srcContent.segment, srcContent.byteOffset + offset, src._capnp.depthLimit - 1);
+ const dstPtr = new Pointer(dstContent.segment, dstContent.byteOffset + offset + 8, dst._capnp.depthLimit - 1);
+
+ copyFrom(srcPtr, dstPtr);
+ }
+ }
+ } else {
+ const byteLength = padToWord(
+ srcElementSize === ListElementSize.BIT
+ ? (srcLength + 7) >>> 3
+ : getListElementByteLength(srcElementSize) * srcLength
+ );
+ const wordLength = byteLength >>> 3;
+
+ dstContent = dst.segment.allocate(byteLength);
+
+ // Copy all of the list contents word-by-word.
+
+ dstContent.segment.copyWords(dstContent.byteOffset, srcContent.segment, srcContent.byteOffset, wordLength);
+ }
+
+ // Initialize the list pointer.
+
+ const res = initPointer(dstContent.segment, dstContent.byteOffset, dst);
+ setListPointer(res.offsetWords, srcElementSize, srcLength, res.pointer, srcCompositeSize);
+}
+
+export function copyFromStruct(src: Pointer, dst: Pointer): void {
+ if (dst._capnp.depthLimit <= 0) throw new Error(PTR_DEPTH_LIMIT_EXCEEDED);
+
+ const srcContent = getContent(src);
+ const srcSize = getTargetStructSize(src);
+ const srcDataWordLength = getDataWordLength(srcSize);
+
+ // Allocate space for the destination content.
+
+ const dstContent = dst.segment.allocate(getByteLength(srcSize));
+
+ // Copy the data section.
+
+ dstContent.segment.copyWords(dstContent.byteOffset, srcContent.segment, srcContent.byteOffset, srcDataWordLength);
+
+ // Copy the pointer section.
+
+ for (let i = 0; i < srcSize.pointerLength; i++) {
+ const offset = srcSize.dataByteLength + i * 8;
+
+ const srcPtr = new Pointer(srcContent.segment, srcContent.byteOffset + offset, src._capnp.depthLimit - 1);
+ const dstPtr = new Pointer(dstContent.segment, dstContent.byteOffset + offset, dst._capnp.depthLimit - 1);
+
+ copyFrom(srcPtr, dstPtr);
+ }
+
+ // Don't touch dst if it's already initialized as a composite list pointer. With composite struct pointers there's
+ // no pointer to copy here and we've already copied the contents.
+
+ if (dst._capnp.compositeList) return;
+
+ // Initialize the struct pointer.
+
+ const res = initPointer(dstContent.segment, dstContent.byteOffset, dst);
+ setStructPointer(res.offsetWords, srcSize, res.pointer);
+}
+
+/**
+ * Track the allocation of a new Pointer object.
+ *
+ * This will decrement an internal counter tracking how many bytes have been traversed in the message so far. After
+ * a certain limit, this method will throw an error in order to prevent a certain class of DoS attacks.
+ *
+ * @param {Message} message The message the pointer belongs to.
+ * @param {Pointer} p The pointer being allocated.
+ * @returns {void}
+ */
+
+export function trackPointerAllocation(message: Message, p: Pointer): void {
+ message._capnp.traversalLimit -= 8;
+
+ if (message._capnp.traversalLimit <= 0) {
+ throw new Error(format(PTR_TRAVERSAL_LIMIT_EXCEEDED, p));
+ }
+}