fix(vcs): avoid unbounded diff memory usage (#25581)

4 files changed, 332 insertions, 65 deletions

diff --git a/packages/opencode/src/git/index.ts b/packages/opencode/src/git/index.ts
index 16a862447..fff1d70b2 100644
--- a/packages/opencode/src/git/index.ts
+++ b/packages/opencode/src/git/index.ts
@@ -24,6 +24,7 @@ const fail = (err: unknown) =>
     text: () => "",
     stdout: Buffer.alloc(0),
     stderr: Buffer.from(err instanceof Error ? err.message : String(err)),
+    truncated: false,
   }) satisfies Result
 
 export type Kind = "added" | "deleted" | "modified"
@@ -45,16 +46,28 @@ export type Stat = {
   readonly deletions: number
 }
 
+export type Patch = {
+  readonly text: string
+  readonly truncated: boolean
+}
+
+export interface PatchOptions {
+  readonly context?: number
+  readonly maxOutputBytes?: number
+}
+
 export interface Result {
   readonly exitCode: number
   readonly text: () => string
   readonly stdout: Buffer
   readonly stderr: Buffer
+  readonly truncated: boolean
 }
 
 export interface Options {
   readonly cwd: string
   readonly env?: Record<string, string>
+  readonly maxOutputBytes?: number
 }
 
 export interface Interface {
@@ -68,6 +81,10 @@ export interface Interface {
   readonly status: (cwd: string) => Effect.Effect<Item[]>
   readonly diff: (cwd: string, ref: string) => Effect.Effect<Item[]>
   readonly stats: (cwd: string, ref: string) => Effect.Effect<Stat[]>
+  readonly patch: (cwd: string, ref: string, file: string, options?: PatchOptions) => Effect.Effect<Patch>
+  readonly patchAll: (cwd: string, ref: string, options?: PatchOptions) => Effect.Effect<Patch>
+  readonly patchUntracked: (cwd: string, file: string, options?: PatchOptions) => Effect.Effect<Patch>
+  readonly statUntracked: (cwd: string, file: string) => Effect.Effect<Stat | undefined>
 }
 
 const kind = (code: string): Kind => {
@@ -96,15 +113,31 @@ export const layer = Layer.effect(
           stderr: "pipe",
         })
         const handle = yield* spawner.spawn(proc)
-        const [stdout, stderr] = yield* Effect.all(
-          [Stream.mkString(Stream.decodeText(handle.stdout)), Stream.mkString(Stream.decodeText(handle.stderr))],
-          { concurrency: 2 },
-        )
+        const collect = (stream: typeof handle.stdout) =>
+          Stream.runFold(
+            stream,
+            () => ({ chunks: [] as Uint8Array[], bytes: 0, truncated: false }),
+            (acc, chunk) => {
+              if (opts.maxOutputBytes === undefined) {
+                acc.chunks.push(chunk)
+                acc.bytes += chunk.length
+                return acc
+              }
+
+              const remaining = opts.maxOutputBytes - acc.bytes
+              if (remaining > 0) acc.chunks.push(remaining >= chunk.length ? chunk : chunk.slice(0, remaining))
+              acc.bytes += chunk.length
+              acc.truncated = acc.truncated || acc.bytes > opts.maxOutputBytes
+              return acc
+            },
+          ).pipe(Effect.map((x) => ({ buffer: Buffer.concat(x.chunks), truncated: x.truncated })))
+        const [stdout, stderr] = yield* Effect.all([collect(handle.stdout), collect(handle.stderr)], { concurrency: 2 })
         return {
           exitCode: yield* handle.exitCode,
-          text: () => stdout,
-          stdout: Buffer.from(stdout),
-          stderr: Buffer.from(stderr),
+          text: () => stdout.buffer.toString("utf8"),
+          stdout: stdout.buffer,
+          stderr: stderr.buffer,
+          truncated: stdout.truncated || stderr.truncated,
         } satisfies Result
       },
       Effect.scoped,
@@ -240,6 +273,61 @@ export const layer = Layer.effect(
       })
     })
 
+    const patch = Effect.fn("Git.patch")(function* (cwd: string, ref: string, file: string, options?: PatchOptions) {
+      const result = yield* run(
+        ["diff", "--patch", "--no-ext-diff", "--no-renames", `--unified=${options?.context ?? 3}`, ref, "--", file],
+        { cwd, maxOutputBytes: options?.maxOutputBytes },
+      )
+      return { text: result.truncated ? "" : result.text(), truncated: result.truncated } satisfies Patch
+    })
+
+    const patchAll = Effect.fn("Git.patchAll")(function* (cwd: string, ref: string, options?: PatchOptions) {
+      const result = yield* run(
+        ["diff", "--patch", "--no-ext-diff", "--no-renames", `--unified=${options?.context ?? 3}`, ref, "--", "."],
+        { cwd, maxOutputBytes: options?.maxOutputBytes },
+      )
+      return { text: result.text(), truncated: result.truncated } satisfies Patch
+    })
+
+    const patchUntracked = Effect.fn("Git.patchUntracked")(function* (
+      cwd: string,
+      file: string,
+      options?: PatchOptions,
+    ) {
+      const result = yield* run(
+        [
+          "diff",
+          "--no-index",
+          "--patch",
+          "--no-ext-diff",
+          "--no-renames",
+          `--unified=${options?.context ?? 3}`,
+          "--",
+          "/dev/null",
+          file,
+        ],
+        { cwd, maxOutputBytes: options?.maxOutputBytes },
+      )
+      return { text: result.truncated ? "" : result.text(), truncated: result.truncated } satisfies Patch
+    })
+
+    const statUntracked = Effect.fn("Git.statUntracked")(function* (cwd: string, file: string) {
+      const result = yield* run(["diff", "--no-index", "--numstat", "--", "/dev/null", file], {
+        cwd,
+        maxOutputBytes: 4096,
+      })
+      if (result.truncated) return
+      const parts = result.text().split("\t")
+      if (parts.length < 2) return
+      const additions = parts[0] === "-" ? 0 : Number.parseInt(parts[0] || "0", 10)
+      const deletions = parts[1] === "-" ? 0 : Number.parseInt(parts[1] || "0", 10)
+      return {
+        file,
+        additions: Number.isFinite(additions) ? additions : 0,
+        deletions: Number.isFinite(deletions) ? deletions : 0,
+      } satisfies Stat
+    })
+
     return Service.of({
       run,
       branch,
@@ -251,6 +339,10 @@ export const layer = Layer.effect(
       status,
       diff,
       stats,
+      patch,
+      patchAll,
+      patchUntracked,
+      statUntracked,
     })
   }),
 )
diff --git a/packages/opencode/src/project/vcs.ts b/packages/opencode/src/project/vcs.ts
index 24112cf44..28ac143ee 100644
--- a/packages/opencode/src/project/vcs.ts
+++ b/packages/opencode/src/project/vcs.ts
@@ -1,10 +1,8 @@
 import { Effect, Layer, Context, Schema, Stream, Scope } from "effect"
 import { formatPatch, structuredPatch } from "diff"
-import path from "path"
 import { Bus } from "@/bus"
 import { BusEvent } from "@/bus/bus-event"
 import { InstanceState } from "@/effect/instance-state"
-import { AppFileSystem } from "@opencode-ai/core/filesystem"
 import { FileWatcher } from "@/file/watcher"
 import { Git } from "@/git"
 import * as Log from "@opencode-ai/core/util/log"
@@ -12,20 +10,11 @@ import { zod } from "@/util/effect-zod"
 import { NonNegativeInt, withStatics } from "@/util/schema"
 
 const log = Log.create({ service: "vcs" })
+const PATCH_CONTEXT_LINES = 2_147_483_647
+const MAX_PATCH_BYTES = 10_000_000
+const MAX_TOTAL_PATCH_BYTES = 10_000_000
 
-const count = (text: string) => {
-  if (!text) return 0
-  if (!text.endsWith("\n")) return text.split("\n").length
-  return text.slice(0, -1).split("\n").length
-}
-
-const work = Effect.fnUntraced(function* (fs: AppFileSystem.Interface, cwd: string, file: string) {
-  const full = path.join(cwd, file)
-  if (!(yield* fs.exists(full).pipe(Effect.orDie))) return ""
-  const buf = yield* fs.readFile(full).pipe(Effect.catch(() => Effect.succeed(new Uint8Array())))
-  if (Buffer.from(buf).includes(0)) return ""
-  return Buffer.from(buf).toString("utf8")
-})
+const emptyPatch = (file: string) => formatPatch(structuredPatch(file, file, "", "", "", "", { context: 0 }))
 
 const nums = (list: Git.Stat[]) =>
   new Map(list.map((item) => [item.file, { additions: item.additions, deletions: item.deletions }] as const))
@@ -38,59 +27,168 @@ const merge = (...lists: Git.Item[][]) => {
   return [...out.values()]
 }
 
-const files = Effect.fnUntraced(function* (
-  fs: AppFileSystem.Interface,
+const emptyBatch = () => ({ patches: new Map<string, string>(), capped: false })
+
+const parseQuotedPath = (value: string) => {
+  let out = ""
+  for (let idx = 1; idx < value.length; idx++) {
+    const char = value[idx]
+    if (char === '"') return { value: out, end: idx + 1 }
+    if (char !== "\\") {
+      out += char
+      continue
+    }
+
+    const next = value[++idx]
+    if (next === "t") out += "\t"
+    else if (next === "n") out += "\n"
+    else if (next === "r") out += "\r"
+    else if (next === '"' || next === "\\") out += next
+    else out += next ?? ""
+  }
+}
+
+const parsePathToken = (value: string) => {
+  if (!value.startsWith('"')) return value.split("\t")[0]
+  return parseQuotedPath(value)?.value ?? value
+}
+
+const fileFromDiffPath = (value: string | undefined) => {
+  if (!value || value === "/dev/null") return
+  const file = parsePathToken(value)
+  if (file.startsWith("a/") || file.startsWith("b/")) return file.slice(2)
+  return file
+}
+
+const fileFromGitHeader = (header: string) => {
+  if (header.startsWith('"')) {
+    const first = parseQuotedPath(header)
+    const second = first ? header.slice(first.end).trimStart() : undefined
+    if (!second) return
+    if (!second.startsWith('"')) return fileFromDiffPath(second)
+    return fileFromDiffPath(parseQuotedPath(second)?.value)
+  }
+
+  const separator = header.indexOf(" b/")
+  if (separator === -1) return
+  return fileFromDiffPath(header.slice(separator + 1))
+}
+
+const fileFromPatchChunk = (chunk: string) => {
+  const next = /^\+\+\+ (.+)$/m.exec(chunk)?.[1]
+  const before = /^--- (.+)$/m.exec(chunk)?.[1]
+  const file = fileFromDiffPath(next) ?? fileFromDiffPath(before)
+  if (file) return file
+
+  const header = /^diff --git (.+)$/m.exec(chunk)?.[1]
+  return fileFromGitHeader(header ?? "")
+}
+
+const splitGitPatch = (patch: Git.Patch) => {
+  const starts = [...patch.text.matchAll(/^diff --git /gm)].map((match) => match.index)
+  const chunks = starts.map((start, index) => patch.text.slice(start, starts[index + 1] ?? patch.text.length))
+  if (!patch.truncated) return chunks
+  return chunks.slice(0, -1)
+}
+
+const batchPatches = Effect.fnUntraced(function* (git: Git.Interface, cwd: string, ref: string, list: Git.Item[]) {
+  if (list.length === 0) return { patches: new Map<string, string>(), capped: false }
+
+  const result = yield* git.patchAll(cwd, ref, {
+    context: PATCH_CONTEXT_LINES,
+    maxOutputBytes: MAX_TOTAL_PATCH_BYTES,
+  })
+  if (result.truncated) log.warn("batched patch exceeded byte limit", { max: MAX_TOTAL_PATCH_BYTES })
+
+  return {
+    patches: splitGitPatch(result).reduce((acc, patch, index) => {
+      const file = fileFromPatchChunk(patch) ?? list[index]?.file
+      if (!file) return acc
+      acc.set(file, (acc.get(file) ?? "") + patch)
+      return acc
+    }, new Map<string, string>()),
+    capped: result.truncated,
+  }
+})
+
+const nativePatch = Effect.fnUntraced(function* (
   git: Git.Interface,
   cwd: string,
   ref: string | undefined,
-  list: Git.Item[],
-  map: Map<string, { additions: number; deletions: number }>,
+  item: Git.Item,
 ) {
-  const base = ref ? yield* git.prefix(cwd) : ""
-  const patch = (file: string, before: string, after: string) =>
-    formatPatch(structuredPatch(file, file, before, after, "", "", { context: Number.MAX_SAFE_INTEGER }))
-  const next = yield* Effect.forEach(
-    list,
-    (item) =>
-      Effect.gen(function* () {
-        const before = item.status === "added" || !ref ? "" : yield* git.show(cwd, ref, item.file, base)
-        const after = item.status === "deleted" ? "" : yield* work(fs, cwd, item.file)
-        const stat = map.get(item.file)
-        return {
-          file: item.file,
-          patch: patch(item.file, before, after),
-          additions: stat?.additions ?? (item.status === "added" ? count(after) : 0),
-          deletions: stat?.deletions ?? (item.status === "deleted" ? count(before) : 0),
-          status: item.status,
-        } satisfies FileDiff
-      }),
-    { concurrency: 8 },
-  )
-  return next.toSorted((a, b) => a.file.localeCompare(b.file))
+  const result =
+    item.code === "??" || !ref
+      ? yield* git.patchUntracked(cwd, item.file, { context: PATCH_CONTEXT_LINES, maxOutputBytes: MAX_PATCH_BYTES })
+      : yield* git.patch(cwd, ref, item.file, { context: PATCH_CONTEXT_LINES, maxOutputBytes: MAX_PATCH_BYTES })
+  if (!result.truncated && result.text) return result.text
+
+  if (result.truncated) log.warn("patch exceeded byte limit", { file: item.file, max: MAX_PATCH_BYTES })
+  return emptyPatch(item.file)
 })
 
-const track = Effect.fnUntraced(function* (
-  fs: AppFileSystem.Interface,
+const totalPatch = (file: string, patch: string, total: number) => {
+  if (total + Buffer.byteLength(patch) <= MAX_TOTAL_PATCH_BYTES) return { patch, capped: false }
+  log.warn("total patch budget exceeded", { file, max: MAX_TOTAL_PATCH_BYTES })
+  return { patch: emptyPatch(file), capped: true }
+}
+
+const patchForItem = Effect.fnUntraced(function* (
   git: Git.Interface,
   cwd: string,
   ref: string | undefined,
+  item: Git.Item,
+  batch: { patches: Map<string, string>; capped: boolean },
+  capped: boolean,
 ) {
-  if (!ref) return yield* files(fs, git, cwd, ref, yield* git.status(cwd), new Map())
-  const [list, stats] = yield* Effect.all([git.status(cwd), git.stats(cwd, ref)], { concurrency: 2 })
-  return yield* files(fs, git, cwd, ref, list, nums(stats))
+  if (capped) return emptyPatch(item.file)
+
+  const batched = batch.patches.get(item.file)
+  if (batched !== undefined) return batched
+  if (item.code !== "??" && batch.capped) return emptyPatch(item.file)
+  return yield* nativePatch(git, cwd, ref, item)
 })
 
-const compare = Effect.fnUntraced(function* (
-  fs: AppFileSystem.Interface,
+const files = Effect.fnUntraced(function* (
   git: Git.Interface,
   cwd: string,
-  ref: string,
+  ref: string | undefined,
+  list: Git.Item[],
+  map: Map<string, { additions: number; deletions: number }>,
+  batch: { patches: Map<string, string>; capped: boolean },
 ) {
+  const next: FileDiff[] = []
+  let total = 0
+  let capped = false
+
+  for (const item of list.toSorted((a, b) => a.file.localeCompare(b.file))) {
+    const stat = map.get(item.file) ?? (item.status === "added" ? yield* git.statUntracked(cwd, item.file) : undefined)
+    const patch = yield* patchForItem(git, cwd, ref, item, batch, capped)
+    const result: { patch: string; capped: boolean } = capped
+      ? { patch, capped: true }
+      : totalPatch(item.file, patch, total)
+    capped = capped || result.capped
+    if (!capped) {
+      total += Buffer.byteLength(result.patch)
+      capped = total >= MAX_TOTAL_PATCH_BYTES
+    }
+    next.push({
+      file: item.file,
+      patch: result.patch,
+      additions: stat?.additions ?? 0,
+      deletions: stat?.deletions ?? 0,
+      status: item.status,
+    })
+  }
+
+  return next
+})
+
+const diffAgainstRef = Effect.fnUntraced(function* (git: Git.Interface, cwd: string, ref: string) {
   const [list, stats, extra] = yield* Effect.all([git.diff(cwd, ref), git.stats(cwd, ref), git.status(cwd)], {
     concurrency: 3,
   })
   return yield* files(
-    fs,
     git,
     cwd,
     ref,
@@ -99,9 +197,15 @@ const compare = Effect.fnUntraced(function* (
       extra.filter((item) => item.code === "??"),
     ),
     nums(stats),
+    yield* batchPatches(git, cwd, ref, list),
   )
 })
 
+const track = Effect.fnUntraced(function* (git: Git.Interface, cwd: string, ref: string | undefined) {
+  if (!ref) return yield* files(git, cwd, ref, yield* git.status(cwd), new Map(), emptyBatch())
+  return yield* diffAgainstRef(git, cwd, ref)
+})
+
 export const Mode = Schema.Literals(["git", "branch"]).pipe(withStatics((s) => ({ zod: zod(s) })))
 export type Mode = Schema.Schema.Type<typeof Mode>
 
@@ -147,10 +251,9 @@ interface State {
 
 export class Service extends Context.Service<Service, Interface>()("@opencode/Vcs") {}
 
-export const layer: Layer.Layer<Service, never, AppFileSystem.Service | Git.Service | Bus.Service> = Layer.effect(
+export const layer: Layer.Layer<Service, never, Git.Service | Bus.Service> = Layer.effect(
   Service,
   Effect.gen(function* () {
-    const fs = yield* AppFileSystem.Service
     const git = yield* Git.Service
     const bus = yield* Bus.Service
     const scope = yield* Scope.Scope
@@ -204,23 +307,19 @@ export const layer: Layer.Layer<Service, never, AppFileSystem.Service | Git.Serv
         const ctx = yield* InstanceState.context
         if (ctx.project.vcs !== "git") return []
         if (mode === "git") {
-          return yield* track(fs, git, ctx.directory, (yield* git.hasHead(ctx.directory)) ? "HEAD" : undefined)
+          return yield* track(git, ctx.directory, (yield* git.hasHead(ctx.directory)) ? "HEAD" : undefined)
         }
 
         if (!value.root) return []
         if (value.current && value.current === value.root.name) return []
         const ref = yield* git.mergeBase(ctx.directory, value.root.ref)
         if (!ref) return []
-        return yield* compare(fs, git, ctx.directory, ref)
+        return yield* diffAgainstRef(git, ctx.directory, ref)
       }),
     })
   }),
 )
 
-export const defaultLayer = layer.pipe(
-  Layer.provide(Git.defaultLayer),
-  Layer.provide(AppFileSystem.defaultLayer),
-  Layer.provide(Bus.layer),
-)
+export const defaultLayer = layer.pipe(Layer.provide(Git.defaultLayer), Layer.provide(Bus.layer))
 
 export * as Vcs from "./vcs"
diff --git a/packages/opencode/test/git/git.test.ts b/packages/opencode/test/git/git.test.ts
index a897a38e6..1e56865d7 100644
--- a/packages/opencode/test/git/git.test.ts
+++ b/packages/opencode/test/git/git.test.ts
@@ -114,6 +114,53 @@ describe("Git", () => {
     })
   })
 
+  test("patch() returns capped native patch output", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await fs.writeFile(path.join(tmp.path, weird), "before\n", "utf-8")
+    await fs.writeFile(path.join(tmp.path, "other.txt"), "old\n", "utf-8")
+    await $`git add .`.cwd(tmp.path).quiet()
+    await $`git commit --no-gpg-sign -m "add file"`.cwd(tmp.path).quiet()
+    await fs.writeFile(path.join(tmp.path, weird), "after\n", "utf-8")
+    await fs.writeFile(path.join(tmp.path, "other.txt"), "new\n", "utf-8")
+
+    await withGit(async (rt) => {
+      const [patch, all, capped] = await Promise.all([
+        rt.runPromise(Git.Service.use((git) => git.patch(tmp.path, "HEAD", weird, { context: 2_147_483_647 }))),
+        rt.runPromise(Git.Service.use((git) => git.patchAll(tmp.path, "HEAD", { context: 2_147_483_647 }))),
+        rt.runPromise(Git.Service.use((git) => git.patch(tmp.path, "HEAD", weird, { maxOutputBytes: 1 }))),
+      ])
+
+      expect(patch.truncated).toBe(false)
+      expect(patch.text).toContain("diff --git")
+      expect(patch.text).toContain("-before")
+      expect(patch.text).toContain("+after")
+      expect(all.truncated).toBe(false)
+      expect(all.text).toContain("diff --git")
+      expect(all.text).toContain("other.txt")
+      expect(all.text).toContain("+new")
+      expect(capped.truncated).toBe(true)
+      expect(capped.text).toBe("")
+    })
+  })
+
+  test("patchUntracked() and statUntracked() handle added files", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await fs.writeFile(path.join(tmp.path, weird), "one\ntwo\n", "utf-8")
+
+    await withGit(async (rt) => {
+      const [patch, stat] = await Promise.all([
+        rt.runPromise(Git.Service.use((git) => git.patchUntracked(tmp.path, weird, { context: 2_147_483_647 }))),
+        rt.runPromise(Git.Service.use((git) => git.statUntracked(tmp.path, weird))),
+      ])
+
+      expect(patch.truncated).toBe(false)
+      expect(patch.text).toContain("diff --git")
+      expect(patch.text).toContain("+one")
+      expect(patch.text).toContain("+two")
+      expect(stat).toEqual(expect.objectContaining({ file: weird, additions: 2, deletions: 0 }))
+    })
+  })
+
   test("show() returns empty text for binary blobs", async () => {
     await using tmp = await tmpdir({ git: true })
     await fs.writeFile(path.join(tmp.path, "bin.dat"), new Uint8Array([0, 1, 2, 3]))
diff --git a/packages/opencode/test/project/vcs.test.ts b/packages/opencode/test/project/vcs.test.ts
index 6fb0e251d..53ff547ac 100644
--- a/packages/opencode/test/project/vcs.test.ts
+++ b/packages/opencode/test/project/vcs.test.ts
@@ -234,6 +234,7 @@ describe("Vcs diff", () => {
           }),
         ]),
       )
+      expect(diff.find((item) => item.file === "file.txt")?.patch).toContain("diff --git")
     })
   })
 
@@ -259,6 +260,34 @@ describe("Vcs diff", () => {
     })
   })
 
+  test("diff('git') keeps batched patches aligned for type changes", async () => {
+    if (process.platform === "win32") return
+
+    await using tmp = await tmpdir({ git: true })
+    await fs.writeFile(path.join(tmp.path, "a.txt"), "old\n", "utf-8")
+    await fs.writeFile(path.join(tmp.path, "b.txt"), "old\n", "utf-8")
+    await $`git add .`.cwd(tmp.path).quiet()
+    await $`git commit --no-gpg-sign -m "add files"`.cwd(tmp.path).quiet()
+    await fs.unlink(path.join(tmp.path, "a.txt"))
+    await fs.symlink("target", path.join(tmp.path, "a.txt"))
+    await fs.writeFile(path.join(tmp.path, "b.txt"), "new\n", "utf-8")
+
+    await withVcsOnly(tmp.path, async () => {
+      const diff = await AppRuntime.runPromise(
+        Effect.gen(function* () {
+          const vcs = yield* Vcs.Service
+          return yield* vcs.diff("git")
+        }),
+      )
+      const a = diff.find((item) => item.file === "a.txt")
+      const b = diff.find((item) => item.file === "b.txt")
+
+      expect(a?.patch).toContain("deleted file mode")
+      expect(a?.patch).toContain("new file mode")
+      expect(b?.patch).toContain("+new")
+    })
+  })
+
   test("diff('branch') returns changes against default branch", async () => {
     await using tmp = await tmpdir({ git: true })
     await $`git branch -M main`.cwd(tmp.path).quiet()