Redirect bundled Bun's c-ares to a reachable resolv.conf (#26)

Bundled Bun's c-ares resolver (its node:http/axios path: WebFetch's
domain preflight, the claude.ai MCP connector, OTEL export) reads the
absolute /etc/resolv.conf. Android maps /etc -> /system/etc, which has
none, so those lookups hang until timeout while Bun's native fetch
(separate DNS) stays fine. Regressed on Claude releases after 2.1.185.

Ship a second freestanding LD_PRELOAD shim, resolv-redirect.so, that
rewrites opens of /etc/resolv.conf to $PREFIX/etc/resolv.conf. c-ares
reads the file via fopen (opaque FILE*), so the shim reaches the real
function through dlsym(RTLD_NEXT, ...); dlsym is left undefined and
resolved from libc.so.6 with no -ldl, so the object carries no
DT_NEEDED (a libdl.so dep would break the glibc ld.so load). The open
family guards its mode va_arg on O_CREAT/O_TMPFILE, fails closed when a
symbol can't be resolved, and the *64 variants are aliases of their
bases. The launcher preloads uname-spoof.so:resolv-redirect.so.

Validated end-to-end on the affected 2.1.198 via the built .deb:
WebFetch goes from the "unable to verify domain" error to success,
while rg/bfs dispatch and startup stay green.

Closes #25

Author: gtbuchanan

AGENTS.md

@@ -27,12 +27,18 @@ publish the binary; the `.deb` contains no Anthropic bytes.
    assignment.
 1. The compiled C launcher (`bin/claude`) execs the patched binary —
    `execv` **preserves `argv[0]`** (so Claude's embedded `grep`/`find`/`rg`
-   dispatch works), it **overwrites `LD_PRELOAD` with the uname shim**
-   (`lib/claude-code-termux/uname-spoof.so`): this both evicts termux-exec's
-   text-script `libc.so` (which the glibc binary's `ld.so` can't load) and
-   preloads a freestanding `uname()` interposer that reports a `< 5.11` kernel,
-   so Bun skips the `epoll_pwait2` path that segfaults at startup on newer
-   kernels (bun#32489 — see `src/uname-shim.c` and `claude-code#50270`). It also
+   dispatch works), it **overwrites `LD_PRELOAD` with two freestanding shims**
+   (`lib/claude-code-termux/uname-spoof.so:…/resolv-redirect.so`): this evicts
+   termux-exec's text-script `libc.so` (which the glibc binary's `ld.so` can't
+   load) and preloads both interposers. The **uname** shim reports a `< 5.11`
+   kernel so Bun skips the `epoll_pwait2` path that segfaults at startup on newer
+   kernels (bun#32489 — see `src/uname-shim.c` and `claude-code#50270`). The
+   **resolv** shim redirects opens of the absolute `/etc/resolv.conf` (which
+   Android maps to the nonexistent `/system/etc/resolv.conf`) to
+   `$PREFIX/etc/resolv.conf`, so bundled Bun's c-ares (its `node:http`/axios
+   path — WebFetch's domain preflight, the claude.ai MCP connector, OTEL export)
+   finds nameservers instead of hanging on a timeout (see `src/resolv-shim.c` and
+   issue #25). It also
    **sets `TMPDIR`/`CLAUDE_CODE_TMPDIR`** to the Termux prefix when unset (Termux
    has no writable `/tmp`; see `src/claude-wrapper.c` for the
    env-vs-hardcoded-`/tmp` analysis and the MCP-browser-bridge limitation,
@@ -65,14 +71,15 @@ publish the binary; the `.deb` contains no Anthropic bytes.
 | `package/payload/libexec/link-native.sh` | Idempotent native-path symlink (`~/.local/bin/claude` → launcher) reconcile, shared by `postinst` and the update command. |
 | `package/payload/libexec/patch-execpath.py` | The `CLAUDE_CODE_EXECPATH` patch. |
 | `package/payload/etc/claude-code-termux.conf` | `CLAUDE_CODE_VERSION` pin + `CLAUDE_CODE_CACHE_DIR` (both empty by default). |
-| `src/claude-wrapper.c` | The C launcher (`-DBINARY=`/`-DTMPDIR_PATH=`/`-DUNAME_SHIM=` baked in at compile). `claude_wrapper_run()` takes its exec function as a parameter — a seam the unit tests fake. |
+| `src/claude-wrapper.c` | The C launcher (`-DBINARY=`/`-DTMPDIR_PATH=`/`-DUNAME_SHIM=`/`-DRESOLV_SHIM=` baked in at compile). `claude_wrapper_run()` takes its exec function as a parameter — a seam the unit tests fake. |
 | `src/uname-shim.c` | Freestanding `LD_PRELOAD` `uname()` interposer reporting kernel `5.10.0`, so Bun avoids the `epoll_pwait2` startup segfault (bun#32489). Built by `build-wrapper.sh`, shipped to `lib/claude-code-termux/uname-spoof.so`, preloaded by the launcher. |
+| `src/resolv-shim.c` | Freestanding `LD_PRELOAD` `fopen`/`open`-family interposer that redirects the absolute `/etc/resolv.conf` (absent on Android) to `$PREFIX/etc/resolv.conf`, so bundled Bun's c-ares resolves DNS on its `node:http` path (WebFetch/claude.ai-MCP/OTEL) instead of hanging (issue #25). References `dlsym` as an undefined symbol resolved from `libc.so.6` — **no `-ldl`**, so zero `DT_NEEDED` (a `libdl.so` dep would break the glibc `ld.so` load). Built by `build-wrapper.sh`, shipped to `lib/claude-code-termux/resolv-redirect.so`, preloaded by the launcher alongside the uname shim. |
 | `test/wrapper_test.c` | Unit tests for the launcher (greatest; recording exec stub). |
 | `test/install_test.sh` | Hermetic unit tests for `install.sh`'s pure helpers (shUnit2; no network/apt). |
 | `test/compat.h` | Test-only `setenv`/`unsetenv` shims for Windows libc; force-included into the test build, never shipped. |
 | `vendor/greatest.h` | Vendored single-header test framework (greatest 1.5.0, ISC; from silentbicycle/greatest). |
 | `vendor/shunit2` | Vendored single-file shell test framework (shUnit2 2.1.9pre, Apache-2.0; pinned to kward/shunit2 master @ `f39734a` — no tagged release since 2.1.8, and master carries the `egrep`→`grep -E` fix we'd otherwise patch). Drives `scripts/e2e.sh` and `test/install_test.sh`. Carries one local patch (grep `PATCHED FOR TERMUX`; re-apply on bump): `#! /bin/sh` stub scripts → resolve `sh` via PATH (submitted upstream as kward/shunit2#189). |
-| `scripts/build-wrapper.sh` | Compile the wrapper + uname shim with Termux's clang. |
+| `scripts/build-wrapper.sh` | Compile the wrapper + uname/resolv shims with Termux's clang. |
 | `scripts/build-deb.sh` | Stage + `dpkg-deb --build` → `artifacts/packages/`. |
 | `scripts/compile.sh` | Compile the wrapper + assemble the `.deb`, in a Termux env. |
 | `scripts/e2e.sh` | Install the prebuilt `.deb` + assert the fixes, in a Termux env. |
@@ -145,11 +152,12 @@ tasks:
 `mise run compile` produces the `.deb`, then `mise run test:e2e` installs it via
 `install.sh` and asserts the real fixes: `argv[0]=rg`/`bfs` dispatch to the
 embedded ripgrep/bfs, startup with `LD_PRELOAD` set (the launcher overwrites it
-with the uname shim), a runtime-init boot guard (`claude mcp list` spins up
+with the two shims), a runtime-init boot guard (`claude mcp list` spins up
 Bun's event loop — catching startup crashes the `--version` fast path can't,
-e.g. the Bun 1.4.0 `epoll_pwait2` segfault the uname shim prevents), `TMPDIR`
-injection, the `settings.json` merge, the conditional/cached update paths, and
-the interpreter-repair `ensure`. The suite is built on the vendored shUnit2 (a
+e.g. the Bun 1.4.0 `epoll_pwait2` segfault the uname shim prevents), the resolv
+redirect (the shim rewrites a configured path and carries no `DT_NEEDED`, #25),
+`TMPDIR` injection, the `settings.json` merge, the conditional/cached update
+paths, and the interpreter-repair `ensure`. The suite is built on the vendored shUnit2 (a
 single sourced file; the install is its `oneTimeSetUp`, behaviors are
 definition-ordered `test_*` functions with the state-mutating ones last). On a
 dev host both tasks dispatch to `scripts/docker-run.sh <script>`, which pulls

README.md

@@ -78,12 +78,15 @@ re-downloaded. Leave it empty (the default) to disable caching.
    (`patch-execpath.py`) so embedded-tool re-execs route back through the
    launcher.
 1. The compiled launcher execs the patched binary, preserving `argv[0]` so
-   Claude's `grep`/`find`/`rg` dispatch works. It overwrites `LD_PRELOAD` with a
-   small `uname` shim: this evicts termux-exec's `libc.so` (which the glibc
-   binary's loader can't load) and reports a `< 5.11` kernel so the bundled Bun
-   skips an `epoll_pwait2` path that otherwise segfaults at startup on newer
-   Android kernels (bun#32489). It also sets `TMPDIR`/`CLAUDE_CODE_TMPDIR` to the
-   Termux prefix (only when unset) since Termux has no writable `/tmp`.
+   Claude's `grep`/`find`/`rg` dispatch works. It overwrites `LD_PRELOAD` with
+   two small shims: this evicts termux-exec's `libc.so` (which the glibc binary's
+   loader can't load) and preloads a `uname` shim that reports a `< 5.11` kernel
+   so the bundled Bun skips an `epoll_pwait2` path that otherwise segfaults at
+   startup on newer Android kernels (bun#32489), plus a `resolv` shim that points
+   Bun's bundled c-ares resolver at `$PREFIX/etc/resolv.conf` (Android has no
+   `/etc/resolv.conf`) so WebFetch, the claude.ai MCP connector, and OTEL export
+   resolve DNS instead of hanging. It also sets `TMPDIR`/`CLAUDE_CODE_TMPDIR` to
+   the Termux prefix (only when unset) since Termux has no writable `/tmp`.
 1. The postinstall also symlinks the launcher onto Anthropic's native-install
    path (`~/.local/bin/claude`) so Claude's health check passes when it detects
    `installMethod: native`. The symlink targets the launcher (not the patched

mise-tasks/test/greatest

@@ -1,8 +1,8 @@
 #!/usr/bin/env bash
 #MISE description="Unit-test the C launcher with greatest natively (fast; no Docker)"
 # Keep Git Bash / MSYS from rewriting the leading-slash sentinel paths
-# (BINARY/TMPDIR_PATH/UNAME_SHIM below) into Windows paths on the way to zig
-# (no-op elsewhere).
+# (BINARY/TMPDIR_PATH/UNAME_SHIM/RESOLV_SHIM below) into Windows paths on the way
+# to zig (no-op elsewhere).
 #MISE env={ MSYS_NO_PATHCONV = "1" }
 #
 # Compiles src/claude-wrapper.c with zig and runs it directly — no Termux, no
@@ -19,6 +19,7 @@ set -euo pipefail
 BINARY=/claude-code-termux-test/claude
 TMPDIR_PATH=/claude-code-termux-test/tmp
 UNAME_SHIM=/claude-code-termux-test/uname-spoof.so
+RESOLV_SHIM=/claude-code-termux-test/resolv-redirect.so
 
 out="$MISE_PROJECT_ROOT/artifacts/build"
 mkdir -p "$out"
@@ -32,7 +33,7 @@ case "${OSTYPE:-}" in msys* | cygwin* | win*) bin="$bin.exe" ;; esac
 # -include compat.h shims setenv/unsetenv on Windows.
 zig cc -O2 -Wall -Wextra -Werror \
   -DBINARY="\"$BINARY\"" -DTMPDIR_PATH="\"$TMPDIR_PATH\"" \
-  -DUNAME_SHIM="\"$UNAME_SHIM\"" \
+  -DUNAME_SHIM="\"$UNAME_SHIM\"" -DRESOLV_SHIM="\"$RESOLV_SHIM\"" \
   -DCLAUDE_WRAPPER_NO_MAIN \
   -include "$MISE_PROJECT_ROOT/test/compat.h" \
   -I "$MISE_PROJECT_ROOT/vendor" \

scripts/build-deb.sh

@@ -45,6 +45,10 @@ stage="$build/${PKG}_${VERSION}_${ARCH}"
   echo "error: $build/uname-spoof.so not found — run build-wrapper.sh first." >&2
   exit 1
 }
+[ -f "$build/resolv-redirect.so" ] || {
+  echo "error: $build/resolv-redirect.so not found — run build-wrapper.sh first." >&2
+  exit 1
+}
 
 # Reset only the staging tree, preserving the compiled wrapper at $build/claude.
 rm -rf "$stage"
@@ -63,8 +67,10 @@ install -d "$stage/$PREFIX_REL/libexec/$PKG"
 install -d "$stage/$PREFIX_REL/etc"
 install -d "$stage/$PREFIX_REL/share/doc/$PKG"
 install -m 0755 "$build/claude" "$stage/$PREFIX_REL/bin/claude"
-# The wrapper LD_PRELOADs this; its baked-in UNAME_SHIM path must match.
+# The wrapper LD_PRELOADs these; their baked-in UNAME_SHIM/RESOLV_SHIM paths
+# must match.
 install -m 0644 "$build/uname-spoof.so" "$stage/$PREFIX_REL/lib/$PKG/uname-spoof.so"
+install -m 0644 "$build/resolv-redirect.so" "$stage/$PREFIX_REL/lib/$PKG/resolv-redirect.so"
 install -m 0755 "$root/package/payload/bin/claude-code-termux-update" "$stage/$PREFIX_REL/bin/claude-code-termux-update"
 install -m 0755 "$root/package/payload/libexec/bootstrap.sh" "$stage/$PREFIX_REL/libexec/$PKG/bootstrap.sh"
 install -m 0755 "$root/package/payload/libexec/link-native.sh" "$stage/$PREFIX_REL/libexec/$PKG/link-native.sh"

scripts/build-wrapper.sh

@@ -11,12 +11,16 @@ set -euo pipefail
 PREFIX=/data/data/com.termux/files/usr
 # The wrapper execs the `current` symlink that bootstrap.sh keeps pointing at
 # the patched binary, sets TMPDIR to the Termux prefix tmp dir (Termux has no
-# writable /tmp), and LD_PRELOADs the uname shim (see src/uname-shim.c). All
-# three are baked in at compile time. UNAME_SHIM must match the install path
-# build-deb.sh stages the .so to.
+# writable /tmp), and LD_PRELOADs two shims (see src/uname-shim.c and
+# src/resolv-shim.c). All are baked in at compile time. UNAME_SHIM/RESOLV_SHIM
+# must match the install paths build-deb.sh stages the .so files to.
 BINARY="$PREFIX/opt/claude-code-termux/current"
 TMPDIR_PATH="$PREFIX/tmp"
 UNAME_SHIM="$PREFIX/lib/claude-code-termux/uname-spoof.so"
+RESOLV_SHIM="$PREFIX/lib/claude-code-termux/resolv-redirect.so"
+# Redirect the absolute /etc/resolv.conf (absent on Android) to the prefix copy.
+RESOLV_SRC="/etc/resolv.conf"
+RESOLV_DST="$PREFIX/etc/resolv.conf"
 
 root=$(cd "$(dirname "$0")/.." && pwd)
 out="$root/artifacts/build"
@@ -31,8 +35,16 @@ mkdir -p "$out"
 "$CC" -O2 -Wall -Wextra -Werror -shared -fPIC -nostdlib -ffreestanding \
   -fno-stack-protector -o "$out/uname-spoof.so" "$root/src/uname-shim.c"
 
+# The resolv shim is freestanding too; it references dlsym (resolved from
+# libc.so.6 — deliberately NO -ldl, so no DT_NEEDED; see src/resolv-shim.c) and
+# needs -fno-builtin so clang doesn't rewrite the interposed fopen/open calls.
+"$CC" -O2 -Wall -Wextra -Werror -shared -fPIC -nostdlib -ffreestanding \
+  -fno-stack-protector -fno-builtin \
+  -DRESOLV_SRC="\"$RESOLV_SRC\"" -DRESOLV_DST="\"$RESOLV_DST\"" \
+  -o "$out/resolv-redirect.so" "$root/src/resolv-shim.c"
+
 "$CC" -O2 -Wall -Wextra -Werror -DBINARY="\"$BINARY\"" -DTMPDIR_PATH="\"$TMPDIR_PATH\"" \
-  -DUNAME_SHIM="\"$UNAME_SHIM\"" \
+  -DUNAME_SHIM="\"$UNAME_SHIM\"" -DRESOLV_SHIM="\"$RESOLV_SHIM\"" \
   -o "$out/claude" "$root/src/claude-wrapper.c"
 
 echo "$out/claude"

scripts/e2e.sh

@@ -95,6 +95,7 @@ oneTimeSetUp() {
   probe="$(mktemp -d)/env"
   clang -O2 -DBINARY="\"$PREFIX/bin/env\"" -DTMPDIR_PATH="\"/PROBE_TMPDIR\"" \
     -DUNAME_SHIM="\"$PREFIX/lib/claude-code-termux/uname-spoof.so\"" \
+    -DRESOLV_SHIM="\"$PREFIX/lib/claude-code-termux/resolv-redirect.so\"" \
     -o "$probe" src/claude-wrapper.c >&2 || fatal "probe compile failed"
 }
 
@@ -106,6 +107,27 @@ test_wrapper_is_elf() {
   assertEquals 'wrapper is an ELF binary' \
     7f454c46 "$(elf_magic "$PREFIX/bin/claude")"
 }
+test_resolv_shim_installed() {
+  assertTrue 'resolv-redirect.so installed' \
+    "[ -f '$PREFIX/lib/claude-code-termux/resolv-redirect.so' ]"
+}
+test_resolv_shim_is_elf() {
+  assertEquals 'resolv-redirect.so is an ELF' \
+    7f454c46 "$(elf_magic "$PREFIX/lib/claude-code-termux/resolv-redirect.so")"
+}
+# The crux of #25: the shim must carry no DT_NEEDED (a libdl.so dep would break
+# the glibc ld.so load; see src/resolv-shim.c). The startup tests catch this
+# end-to-end too, but this pinpoints a regression to the shim.
+test_resolv_shim_has_no_dt_needed() {
+  local needed rc
+  # No 2>/dev/null: a patchelf failure must surface, not be swallowed into an
+  # empty (assertNull-passing) result. Assert it ran before trusting the output.
+  needed=$(LD_PRELOAD='' "$patchelf" --print-needed \
+    "$PREFIX/lib/claude-code-termux/resolv-redirect.so")
+  rc=$?
+  assertEquals 'patchelf --print-needed ran' 0 "$rc"
+  assertNull 'resolv-redirect.so has no DT_NEEDED (no libdl.so)' "$needed"
+}
 test_bootstrap_installed() {
   assertTrue 'bootstrap.sh installed + executable' \
     "[ -x '$PREFIX/libexec/claude-code-termux/bootstrap.sh' ]"
@@ -262,6 +284,43 @@ test_startup_with_ld_preload_set() {
     "LD_PRELOAD='$preload_lib' '$PREFIX/bin/claude' --version >/dev/null 2>&1"
 }
 
+# resolv redirect: compile a shim variant with temp sentinels (the probe
+# pattern) + a tiny opener, then prove fopen(SRC) is rewritten to DST (SRC
+# absent, so an unredirected open misses). Exercises src/resolv-shim.c directly,
+# independent of a c-ares-affected Claude version. See #25.
+test_resolv_redirect_rewrites_configured_path() {
+  local dir src dst rc
+  dir=$(mktemp -d)
+  src="$dir/sys-resolv.conf" # stands in for the absolute /etc/resolv.conf
+  dst="$dir/prefix-resolv.conf"
+  printf 'nameserver 203.0.113.1\n' >"$dst" # marker; src intentionally absent
+  clang -O2 -Wall -Wextra -Werror -shared -fPIC -nostdlib -ffreestanding \
+    -fno-stack-protector -fno-builtin \
+    -DRESOLV_SRC="\"$src\"" -DRESOLV_DST="\"$dst\"" \
+    -o "$dir/resolv-redirect.so" src/resolv-shim.c 2>"$dir/cc.log"
+  rc=$?
+  assertEquals "resolv shim test build ($(cat "$dir/cc.log"))" 0 "$rc"
+  cat >"$dir/opener.c" <<'EOF'
+#include <stdio.h>
+int main(int argc, char **argv) {
+  FILE *f = fopen(argv[1], "r");
+  if (!f) { puts("MISS"); return 1; }
+  char b[64];
+  if (!fgets(b, sizeof b, f)) b[0] = '\0';
+  fputs(b, stdout);
+  fclose(f);
+  return 0;
+}
+EOF
+  clang -O2 -o "$dir/opener" "$dir/opener.c" 2>/dev/null
+  assertEquals 'opener test build' 0 $?
+  assertEquals 'absent source path misses without the shim' \
+    MISS "$("$dir/opener" "$src" 2>&1)"
+  assertContains 'shim redirects fopen(SRC) to the configured target' \
+    "$(LD_PRELOAD="$dir/resolv-redirect.so" "$dir/opener" "$src" 2>&1)" '203.0.113.1'
+  rm -rf "$dir"
+}
+
 # TMPDIR injection: Termux has no writable /tmp, so the wrapper sets TMPDIR +
 # CLAUDE_CODE_TMPDIR (only when unset). The probe (BINARY=env) prints the env the
 # wrapper hands to the exec'd process.

src/claude-wrapper.c

@@ -12,9 +12,9 @@
  * the glibc Claude binary (see the LD_PRELOAD comment in claude_wrapper_run).
  *
  * BINARY (the absolute path to the patched Claude Code binary), TMPDIR_PATH (the
- * Termux prefix tmp dir), and UNAME_SHIM (the absolute path to the uname-spoof
- * .so) are baked in at compile time via -DBINARY="…", -DTMPDIR_PATH="…", and
- * -DUNAME_SHIM="…".
+ * Termux prefix tmp dir), UNAME_SHIM, and RESOLV_SHIM (the absolute paths to the
+ * two LD_PRELOAD shims) are baked in at compile time via -DBINARY="…",
+ * -DTMPDIR_PATH="…", -DUNAME_SHIM="…", and -DRESOLV_SHIM="…".
  */
 #include <errno.h>
 #include <stdio.h>
@@ -35,6 +35,11 @@
     "UNAME_SHIM must be defined at compile time (-DUNAME_SHIM=\"/…/uname-spoof.so\")"
 #endif
 
+#ifndef RESOLV_SHIM
+#error                                                                         \
+    "RESOLV_SHIM must be defined at compile time (-DRESOLV_SHIM=\"/…/resolv-redirect.so\")"
+#endif
+
 /*
  * The launch logic, with the exec call injected as a parameter so unit tests
  * can substitute a fake and observe the (path, argv) handoff — and the env it
@@ -67,14 +72,14 @@ int claude_wrapper_run(int argc, char **argv,
      second, settings-independent layer that travels with every launch.
      overwrite=0 so an explicit user value still wins. */
   (void)setenv("DISABLE_AUTOUPDATER", "1", 0);
-  /* Replace (not clear) LD_PRELOAD with the uname shim. termux-exec's
-     unversioned libc.so text-script crashes the glibc binary's ld.so, so it
-     must not survive into the exec — and overwriting the variable both evicts
-     it and preloads our interposer, which reports a < 5.11 kernel so Bun avoids
-     the epoll_pwait2 startup segfault (bun#32489; see src/uname-shim.c).
-     overwrite=1: whatever was inherited (termux-exec, or a stale value) is
-     intentionally displaced. */
-  (void)setenv("LD_PRELOAD", UNAME_SHIM, 1);
+  /* Replace (not clear) LD_PRELOAD with our two shims. termux-exec's
+     unversioned libc.so text-script would crash the glibc binary's ld.so, so
+     overwriting both evicts it and preloads the interposers: uname-spoof
+     (src/uname-shim.c) and resolv-redirect (src/resolv-shim.c), both
+     freestanding glibc ELFs the ugrep/bfs re-exec tolerates. overwrite=1
+     intentionally displaces whatever was inherited (termux-exec, or a stale
+     value). */
+  (void)setenv("LD_PRELOAD", UNAME_SHIM ":" RESOLV_SHIM, 1);
   exec(BINARY, argv);
   fprintf(stderr, "claude wrapper: execv %s failed: %s\n", BINARY,
           strerror(errno));