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Copy pathdebug-loadobject.ts
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369 lines (315 loc) · 11.2 KB
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/**
* Debug script to trace object loading flow during delta computation
*/
import * as fs from "node:fs/promises";
import * as path from "node:path";
import { promisify } from "node:util";
import { inflate } from "node:zlib";
const inflateAsync = promisify(inflate);
const TEST_REPO = path.join(process.cwd(), "apps/example-git-lifecycle/test-lifecycle-repo/.git");
/**
* Find null byte in buffer
*/
function findNullByte(buf: Uint8Array, maxLen = 32): number {
const limit = Math.min(maxLen, buf.length);
for (let i = 0; i < limit; i++) {
if (buf[i] === 0) return i;
}
return -1;
}
/**
* Parse Git object header
*/
function parseGitHeader(buf: Uint8Array): { type: string; size: number; headerLen: number } | null {
const nullPos = findNullByte(buf);
if (nullPos === -1) return null;
const headerStr = new TextDecoder().decode(buf.subarray(0, nullPos));
const spacePos = headerStr.indexOf(" ");
if (spacePos === -1) return null;
return {
type: headerStr.substring(0, spacePos),
size: parseInt(headerStr.substring(spacePos + 1), 10),
headerLen: nullPos + 1,
};
}
/**
* Load loose object
*/
async function _loadLooseObject(oid: string): Promise<{
raw: Uint8Array;
header: ReturnType<typeof parseGitHeader>;
content: Uint8Array;
} | null> {
const objectPath = path.join(TEST_REPO, "objects", oid.substring(0, 2), oid.substring(2));
try {
const compressed = await fs.readFile(objectPath);
const raw = new Uint8Array(await inflateAsync(compressed));
const header = parseGitHeader(raw);
if (!header) return null;
return {
raw,
header,
content: raw.subarray(header.headerLen),
};
} catch {
return null;
}
}
/**
* Read pack index to find object offset
*/
async function findOffsetInPack(oid: string, idxPath: string): Promise<number> {
const idxData = new Uint8Array(await fs.readFile(idxPath));
// Check for v2 index magic
const magic = (idxData[0] << 24) | (idxData[1] << 16) | (idxData[2] << 8) | idxData[3];
if (magic !== 0xff744f63) {
console.log("Not a v2 index");
return -1;
}
const version = (idxData[4] << 24) | (idxData[5] << 16) | (idxData[6] << 8) | idxData[7];
if (version !== 2) {
console.log(`Unsupported index version: ${version}`);
return -1;
}
// Fanout table at offset 8, 256 entries x 4 bytes
const fanoutStart = 8;
const totalObjects =
(idxData[fanoutStart + 255 * 4] << 24) |
(idxData[fanoutStart + 255 * 4 + 1] << 16) |
(idxData[fanoutStart + 255 * 4 + 2] << 8) |
idxData[fanoutStart + 255 * 4 + 3];
// SHA-1 table starts after fanout
const sha1Start = fanoutStart + 256 * 4;
// Binary search in SHA-1 table
const oidBytes = new Uint8Array(20);
for (let i = 0; i < 20; i++) {
oidBytes[i] = parseInt(oid.substring(i * 2, i * 2 + 2), 16);
}
let lo = 0;
let hi = totalObjects;
const firstByte = oidBytes[0];
if (firstByte > 0) {
lo =
(idxData[fanoutStart + (firstByte - 1) * 4] << 24) |
(idxData[fanoutStart + (firstByte - 1) * 4 + 1] << 16) |
(idxData[fanoutStart + (firstByte - 1) * 4 + 2] << 8) |
idxData[fanoutStart + (firstByte - 1) * 4 + 3];
}
hi =
(idxData[fanoutStart + firstByte * 4] << 24) |
(idxData[fanoutStart + firstByte * 4 + 1] << 16) |
(idxData[fanoutStart + firstByte * 4 + 2] << 8) |
idxData[fanoutStart + firstByte * 4 + 3];
while (lo < hi) {
const mid = Math.floor((lo + hi) / 2);
const entryOffset = sha1Start + mid * 20;
let cmp = 0;
for (let i = 0; i < 20 && cmp === 0; i++) {
cmp = oidBytes[i] - idxData[entryOffset + i];
}
if (cmp === 0) {
// Found! Read offset from offset table
// CRC table follows SHA-1 table
const crcStart = sha1Start + totalObjects * 20;
// 4-byte offset table follows CRC table
const offsetStart = crcStart + totalObjects * 4;
const offsetEntry = offsetStart + mid * 4;
const offset =
(idxData[offsetEntry] << 24) |
(idxData[offsetEntry + 1] << 16) |
(idxData[offsetEntry + 2] << 8) |
idxData[offsetEntry + 3];
return offset;
} else if (cmp < 0) {
hi = mid;
} else {
lo = mid + 1;
}
}
return -1;
}
/**
* Read pack entry header
*/
function readPackEntryHeader(
packData: Uint8Array,
offset: number,
): { type: number; size: number; headerLen: number } {
const b = packData[offset];
const type = (b >> 4) & 0x07;
let size = b & 0x0f;
let shift = 4;
let headerLen = 1;
while ((packData[offset + headerLen - 1] & 0x80) !== 0) {
const c = packData[offset + headerLen];
size |= (c & 0x7f) << shift;
shift += 7;
headerLen++;
}
return { type, size, headerLen };
}
/**
* Load object from pack file
*/
async function _loadPackObject(
oid: string,
): Promise<{ type: number; size: number; content: Uint8Array } | null> {
const packDir = path.join(TEST_REPO, "objects", "pack");
const files = await fs.readdir(packDir);
const packFiles = files.filter((f) => f.endsWith(".pack"));
for (const packFile of packFiles) {
const idxFile = packFile.replace(".pack", ".idx");
const idxPath = path.join(packDir, idxFile);
const packPath = path.join(packDir, packFile);
const offset = await findOffsetInPack(oid, idxPath);
if (offset === -1) continue;
const packData = new Uint8Array(await fs.readFile(packPath));
const header = readPackEntryHeader(packData, offset);
// For non-delta types (1-4), decompress directly
if (header.type >= 1 && header.type <= 4) {
// Decompress content
const compressedStart = offset + header.headerLen;
const maxCompressed = Math.min(packData.length - compressedStart, header.size * 3 + 1024);
const compressed = packData.slice(compressedStart, compressedStart + maxCompressed);
try {
const content = new Uint8Array(await inflateAsync(compressed));
return { type: header.type, size: header.size, content };
} catch (e) {
console.log(`Failed to decompress: ${e}`);
return null;
}
}
console.log(`Object ${oid} is delta type ${header.type}`);
return null;
}
return null;
}
async function main() {
console.log("Debug: Object loading flow analysis\n");
// Find a pack file
const packDir = path.join(TEST_REPO, "objects", "pack");
let packFiles: string[];
try {
packFiles = (await fs.readdir(packDir)).filter((f) => f.endsWith(".pack"));
} catch {
console.log("No pack directory found");
return;
}
if (packFiles.length === 0) {
console.log("No pack files found");
return;
}
console.log(`Found ${packFiles.length} pack file(s): ${packFiles.join(", ")}\n`);
// Load pack and find a non-delta blob
const packPath = path.join(packDir, packFiles[0]);
const packData = new Uint8Array(await fs.readFile(packPath));
// Skip header
const objectCount =
(packData[8] << 24) | (packData[9] << 16) | (packData[10] << 8) | packData[11];
console.log(`Pack has ${objectCount} objects\n`);
// Find blob at offset 316 (from analysis)
const testOffset = 316;
const header = readPackEntryHeader(packData, testOffset);
console.log(`Object at offset ${testOffset}:`);
console.log(
` Type code: ${header.type} (${["", "commit", "tree", "blob", "tag"][header.type] || "unknown"})`,
);
console.log(` Size: ${header.size}`);
console.log(` Header length: ${header.headerLen}`);
// Decompress
const compressedStart = testOffset + header.headerLen;
const maxCompressed = Math.min(packData.length - compressedStart, header.size * 3 + 1024);
const compressed = packData.slice(compressedStart, compressedStart + maxCompressed);
try {
const content = new Uint8Array(await inflateAsync(compressed));
console.log(` Decompressed size: ${content.length}`);
console.log(` First 50 bytes: ${new TextDecoder().decode(content.subarray(0, 50))}`);
// Now simulate what loadRaw does
const typeNames = ["", "commit", "tree", "blob", "tag"];
const typeName = typeNames[header.type];
const gitHeader = `${typeName} ${content.length}\0`;
const gitHeaderBytes = new TextEncoder().encode(gitHeader);
console.log(`\nSimulated loadRaw output:`);
console.log(
` Git header: "${typeName} ${content.length}\\0" (${gitHeaderBytes.length} bytes)`,
);
console.log(` Total with header: ${gitHeaderBytes.length + content.length} bytes`);
// Simulate stripGitHeader
const withHeader = new Uint8Array(gitHeaderBytes.length + content.length);
withHeader.set(gitHeaderBytes, 0);
withHeader.set(content, gitHeaderBytes.length);
const nullPos = findNullByte(withHeader);
console.log(` Null byte position: ${nullPos}`);
const stripped = withHeader.subarray(nullPos + 1);
console.log(` After stripping header: ${stripped.length} bytes`);
// Compare
console.log(`\nComparison:`);
console.log(` Stored content size: ${header.size}`);
console.log(` Decompressed size: ${content.length}`);
console.log(` After strip: ${stripped.length}`);
console.log(` Match: ${content.length === stripped.length ? "YES" : "NO"}`);
} catch (e) {
console.log(` Failed to decompress: ${e}`);
}
// Now let's look at a delta and its base
console.log(`\n${"=".repeat(60)}`);
console.log(`Analyzing delta at offset 5746`);
const deltaOffset = 5746;
const deltaHeader = readPackEntryHeader(packData, deltaOffset);
console.log(` Type code: ${deltaHeader.type}`);
console.log(` Size: ${deltaHeader.size}`);
if (deltaHeader.type === 6) {
// OFS_DELTA - read offset
let ofs = 0;
let pos = deltaOffset + deltaHeader.headerLen;
let c = packData[pos++];
ofs = c & 0x7f;
while ((c & 0x80) !== 0) {
ofs += 1;
ofs <<= 7;
c = packData[pos++];
ofs |= c & 0x7f;
}
const baseOffset = deltaOffset - ofs;
console.log(` Base offset: ${baseOffset} (current - ${ofs})`);
// Decompress delta
const deltaCompressedStart = pos;
const deltaMaxCompressed = Math.min(packData.length - deltaCompressedStart, 4096);
const deltaCompressed = packData.slice(
deltaCompressedStart,
deltaCompressedStart + deltaMaxCompressed,
);
try {
const deltaContent = new Uint8Array(await inflateAsync(deltaCompressed));
console.log(` Delta content size: ${deltaContent.length}`);
// Read base size from delta header
let p = 0;
let baseSize = 0;
let shift = 0;
let ch: number;
do {
ch = deltaContent[p++];
baseSize |= (ch & 0x7f) << shift;
shift += 7;
} while ((ch & 0x80) !== 0);
let resultSize = 0;
shift = 0;
do {
ch = deltaContent[p++];
resultSize |= (ch & 0x7f) << shift;
shift += 7;
} while ((ch & 0x80) !== 0);
console.log(` Delta header: baseSize=${baseSize}, resultSize=${resultSize}`);
// Load base
const baseHeader = readPackEntryHeader(packData, baseOffset);
console.log(` Base object: type=${baseHeader.type}, size=${baseHeader.size}`);
console.log(
`\n MISMATCH: Delta expects baseSize=${baseSize}, but base has size=${baseHeader.size}`,
);
console.log(` Difference: ${baseHeader.size - baseSize} bytes`);
} catch (e) {
console.log(` Failed to decompress delta: ${e}`);
}
}
}
main().catch(console.error);