Add C as a supported output language

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **C# output language**: `output_language: "csharp"` is now supported alongside python/javascript/typescript, generating a minimal .NET project using `System.Net.Http.HttpClient` and `System.Text.Json` (both part of the .NET 5+ base class library — no NuGet dependency needed), with the same auth-hardcoding/refresh guidance as the other languages.
 - **PHP output language**: `output_language: "php"` is now supported alongside python/javascript/typescript, generating a script using the `curl` and `json_encode`/`json_decode` core extensions (`ext-curl`, `ext-json` — no Composer dependency needed), with the same auth-hardcoding/refresh guidance as the other languages.
 - **Ruby output language**: `output_language: "ruby"` is now supported alongside python/javascript/typescript, generating a script using `net/http` and `json` (both part of Ruby's standard library — no gem/Bundler dependency needed), with the same auth-hardcoding/refresh guidance as the other languages.
+- **C output language**: `output_language: "c"` is now supported alongside python/javascript/typescript, generating a program using `libcurl` for HTTP and a vendored `cJSON` for JSON (C has neither in its standard library), compiled and run as a single `{run_command}` step, with the same auth-hardcoding/refresh guidance as the other languages.
 
 ## [0.10.0] - 2026-06-01
 

README.md

@@ -96,7 +96,7 @@ Settings live in `~/.reverse-api/config.json` and can be edited via `/settings`
 
 - **Models**: Sonnet 4.6 (default), Opus 4.6 (most capable), Haiku 4.5 (fastest). For OpenCode see [models.dev](https://models.dev).
 - **SDK**: `claude` (default), `opencode`, `cursor`, or `copilot` (GitHub Copilot).
-- **Output language**: `python`, `javascript`, `typescript`, `go`, `java`, `csharp`, `php`, or `ruby`.
+- **Output language**: `python`, `javascript`, `typescript`, `go`, `java`, `csharp`, `php`, `ruby`, or `c`. C needs a POSIX toolchain (`cc`, libcurl headers) — macOS/Linux, or WSL/MSYS2 on Windows.
 
 ## CLI
 

src/reverse_api/base_engineer.py

@@ -39,6 +39,7 @@ class BaseEngineer(ABC):
         "csharp": ".cs",
         "php": ".php",
         "ruby": ".rb",
+        "c": ".c",
     }
 
     def __init__(
@@ -450,6 +451,7 @@ def _get_language_name(self) -> str:
             "csharp": "C#",
             "php": "PHP",
             "ruby": "Ruby",
+            "c": "C",
         }.get(self.output_language, "Python")
 
     def _get_existing_client_guidance(self) -> str:
@@ -546,6 +548,24 @@ def _get_run_command(self) -> str:
             # pointing this command at the wrong, doubly-nested location.
             path = shlex.quote(str(self.scripts_dir.resolve() / self._get_client_filename()))
             return f"ruby {path}"
+        if self.output_language == "c":
+            # Unlike every other language here, C needs an explicit compile
+            # step before it can run at all — one shell command chains
+            # both. Full paths throughout, not bare relative filenames: the
+            # agent's cwd for the whole session is scripts_dir.parent.parent
+            # (see analyze_and_generate's ClaudeAgentOptions), not
+            # scripts_dir where the source/output actually live.
+            # shlex.quote (not manual double-quoting) so shell metacharacters
+            # in any of these three paths can't be interpreted as command
+            # substitution. .resolve(): a relative --output-dir would
+            # otherwise be re-interpreted against the agent's cwd (scripts_
+            # dir.parent.parent) instead of the original cwd it was relative
+            # to, pointing all three at the wrong, doubly-nested location.
+            resolved = self.scripts_dir.resolve()
+            source = shlex.quote(str(resolved / self._get_client_filename()))
+            cjson = shlex.quote(str(resolved / "cJSON.c"))
+            binary = shlex.quote(str(resolved / "api_client"))
+            return f"cc {source} {cjson} -lcurl -o {binary} && {binary}"
         return {
             "python": "python api_client.py",
             "javascript": "node api_client.js",
@@ -669,6 +689,11 @@ def _get_auto_output_files(self, language_name: str, client_filename: str) -> st
             return base + f"\n3. `{self.scripts_dir}/pom.xml` - Maven project file (Gson dependency, exec-maven-plugin)"
         elif self.output_language == "csharp":
             return base + f"\n3. `{self.scripts_dir}/ApiClient.csproj` - .NET project file"
+        elif self.output_language == "c":
+            return base + (
+                f"\n3. `{self.scripts_dir}/cJSON.c` and `{self.scripts_dir}/cJSON.h` - "
+                "Vendored JSON library"
+            )
         return base
 
     @abstractmethod

src/reverse_api/cli.py

@@ -1088,6 +1088,7 @@ def handle_settings(mode_color=THEME_PRIMARY):
             Choice(title="csharp", value="csharp"),
             Choice(title="php", value="php"),
             Choice(title="ruby", value="ruby"),
+            Choice(title="c", value="c"),
             Choice(title="back", value="back"),
         ]
         lang = questionary.select(

src/reverse_api/config.py

@@ -20,7 +20,7 @@
     "opencode_model": "claude-opus-4-6",
     "opencode_provider": "anthropic",
     "output_dir": None,  # None means use ~/.reverse-api/runs
-    "output_language": "python",  # "python", "javascript", "typescript", "go", "java", "csharp", "php", or "ruby"
+    "output_language": "python",  # "python", "javascript", "typescript", "go", "java", "csharp", "php", "ruby", or "c"
     "real_time_sync": True,  # Enable real-time file sync during engineering
     "sdk": "claude",  # "claude", "opencode", "copilot", or "cursor"
 }

src/reverse_api/engineer.py

@@ -232,7 +232,7 @@ def run_reverse_engineering(
         cursor_setting_sources: Optional explicit list (overrides cursor_web_search), e.g. ["project","user","all"].
         enable_sync: Enable real-time file syncing during engineering
         is_fresh: Whether to start fresh (ignore previous scripts)
-        output_language: Target language - "python", "javascript", "typescript", "go", "java", "csharp", "php", or "ruby"
+        output_language: Target language - "python", "javascript", "typescript", "go", "java", "csharp", "php", "ruby", or "c"
         output_mode: Output mode - "client" for API client code, "docs" for OpenAPI specification
     """
     if sdk == "opencode":

src/reverse_api/prompts/__init__.py

@@ -54,7 +54,7 @@ def load_language_partial(language: str, **kwargs: str) -> str:
     """Load the language-specific codegen instructions partial.
 
     Args:
-        language: One of "python", "javascript", "typescript", "go", "java", "csharp", "php", "ruby".
+        language: One of "python", "javascript", "typescript", "go", "java", "csharp", "php", "ruby", "c".
         **kwargs: Placeholder values (scripts_dir, client_filename, run_command).
     """
     return load(f"partials/_language_{language}", **kwargs)

src/reverse_api/prompts/partials/_language_c.md

@@ -0,0 +1,26 @@
+**Generate a C program** that replicates the API calls found in the traffic. The following are guidelines — use your judgment on what's appropriate for the specific API:
+
+- C has no HTTP client or JSON support in its standard library, unlike every other output language here — use `libcurl` for requests and vendor `cJSON` (a small, widely-used, permissively-licensed single-file JSON library) for JSON, rather than hand-rolling either from scratch
+- Don't hand-write or reconstruct `cJSON.c`/`cJSON.h` from memory — fetch the exact, pinned upstream source instead, so the vendored copy is the real, complete library rather than a possibly incomplete or subtly wrong approximation:
+  - `curl -fsSL -o {scripts_dir}/cJSON.c https://raw.githubusercontent.com/DaveGamble/cJSON/v1.7.18/cJSON.c`
+  - `curl -fsSL -o {scripts_dir}/cJSON.h https://raw.githubusercontent.com/DaveGamble/cJSON/v1.7.18/cJSON.h`
+- `libcurl` itself is a system library this project can't fetch or vendor — if compilation fails because `curl/curl.h` isn't found, stop and report a clear error naming the missing prerequisite (e.g. "libcurl development headers not found — install libcurl4-openssl-dev (Debian/Ubuntu) or curl (Homebrew) and retry") rather than running a package manager yourself; installing system packages is a host change the user should make and confirm, not something to do silently inside an auto-authorized session
+- Reuse one `CURL` handle across requests rather than creating a new one per call
+- Create a separate function for each distinct API endpoint, with a small struct for its response shape
+- Check every `libcurl`/allocation return value; don't ignore errors
+- Include a `main` function with example usage
+
+**Authentication & credentials:**
+- Hardcode all cookies, tokens, session IDs, and auth headers found in the traffic directly in the program
+- The user should be able to run the program immediately with zero configuration — no env vars, no config files, no manual setup beyond what's generated
+- If the API uses cookies, enable `libcurl`'s cookie engine (`CURLOPT_COOKIEFILE`, e.g. pointed at an in-memory/empty string to just turn it on) so cookies persist automatically across requests on the same handle
+- If the API uses Bearer tokens or API keys, hardcode them in the request headers
+- Handle auth refresh so the program doesn't go stale: if you see a token refresh endpoint, OAuth refresh flow, or login endpoint in the traffic, implement automatic re-authentication when a request returns 401/403. If cookies have expiry, re-fetch them before they expire
+
+**Testing:**
+- Unlike every other language here, this needs a compile step before it can run — a single `{run_command}` handles both
+- You have up to 5 attempts to fix issues
+
+Save the program to: `{scripts_dir}/{client_filename}`
+Save documentation to: `{scripts_dir}/README.md`
+Save the vendored JSON library to: `{scripts_dir}/cJSON.c` and `{scripts_dir}/cJSON.h`

tests/test_base_engineer.py

@@ -214,6 +214,10 @@ def test_get_output_extension_ruby(self, tmp_path):
         """Ruby extension."""
         eng = self._make_engineer(tmp_path, output_language="ruby")
         assert eng._get_output_extension() == ".rb"
+    def test_get_output_extension_c(self, tmp_path):
+        """C extension."""
+        eng = self._make_engineer(tmp_path, output_language="c")
+        assert eng._get_output_extension() == ".c"
 
     def test_get_output_extension_unknown(self, tmp_path):
         """Unknown language defaults to .py."""
@@ -378,6 +382,50 @@ def test_get_run_command_ruby_resolves_relative_output_dir(self, tmp_path):
         script_arg = tokens[1]
         assert Path(script_arg).is_absolute()
         assert script_arg == str(eng.scripts_dir.resolve() / "api_client.rb")
+    def test_get_run_command_c(self, tmp_path):
+        """Run command for C compiles and runs as one step, using full,
+        resolved, shell-quoted paths throughout — the agent's cwd is
+        scripts_dir.parent.parent (see analyze_and_generate), not
+        scripts_dir where the source, vendored cJSON, and compiled binary
+        all actually live."""
+        eng = self._make_engineer(tmp_path, output_language="c")
+        resolved = eng.scripts_dir.resolve()
+        source = shlex.quote(str(resolved / "api_client.c"))
+        cjson = shlex.quote(str(resolved / "cJSON.c"))
+        binary = shlex.quote(str(resolved / "api_client"))
+        expected = f"cc {source} {cjson} -lcurl -o {binary} && {binary}"
+        assert eng._get_run_command() == expected
+
+    def test_get_run_command_c_quotes_metacharacters(self, tmp_path):
+        """A scripts_dir containing shell metacharacters must round-trip
+        back to the literal path for all three paths (source, cJSON,
+        binary), not be left open to $()/backtick expansion — what the
+        naive f'"{path}"' approach got wrong."""
+        eng = self._make_engineer(tmp_path, output_language="c")
+        eng.scripts_dir = Path("/tmp/weird$(rm -rf ~) dir")
+        resolved = eng.scripts_dir.resolve()
+        tokens = shlex.split(eng._get_run_command())
+        assert tokens[:2] == ["cc", str(resolved / "api_client.c")]
+        assert tokens[2] == str(resolved / "cJSON.c")
+        assert tokens[3:6] == ["-lcurl", "-o", str(resolved / "api_client")]
+        assert tokens[6] == "&&"
+        assert tokens[7] == str(resolved / "api_client")
+
+    def test_get_run_command_c_resolves_relative_output_dir(self, tmp_path):
+        """A relative scripts_dir must be resolved to an absolute path for
+        all three paths (source, cJSON, binary) before being embedded in
+        the command — otherwise, once the agent's cwd moves to
+        scripts_dir.parent.parent, the same relative string gets
+        re-interpreted from there and points at the wrong, doubly-nested
+        location."""
+        eng = self._make_engineer(tmp_path, output_language="c")
+        eng.scripts_dir = Path("relative_output/scripts/run123")
+        resolved = eng.scripts_dir.resolve()
+        tokens = shlex.split(eng._get_run_command())
+        assert Path(tokens[1]).is_absolute()
+        assert tokens[1] == str(resolved / "api_client.c")
+        assert tokens[2] == str(resolved / "cJSON.c")
+        assert tokens[5] == str(resolved / "api_client")
 
     def test_get_run_command_unknown(self, tmp_path):
         """Unknown language defaults to Python command."""
@@ -454,6 +502,12 @@ def test_ruby_prompt(self, tmp_path):
         system_prompt, user_message = eng._build_prompts()
         assert "Ruby script" in system_prompt
         assert "net/http" in system_prompt
+    def test_c_prompt(self, tmp_path):
+        """C prompt includes C-specific instructions."""
+        eng = self._make_engineer(tmp_path, output_language="c")
+        system_prompt, user_message = eng._build_prompts()
+        assert "C program" in system_prompt
+        assert "libcurl" in system_prompt
 
     def test_docs_prompt(self, tmp_path):
         """Docs mode prompt includes OpenAPI instructions."""

tests/test_prompts.py

@@ -121,6 +121,16 @@ def test_ruby_partial(self):
         assert "Ruby script" in text
         assert "net/http" in text
         assert "/tmp/scripts/api_client.rb" in text
+    def test_c_partial(self):
+        text = load_language_partial(
+            "c",
+            scripts_dir="/tmp/scripts",
+            client_filename="api_client.c",
+            run_command='cc "/tmp/scripts/api_client.c" "/tmp/scripts/cJSON.c" -lcurl -o "/tmp/scripts/api_client" && "/tmp/scripts/api_client"',
+        )
+        assert "C program" in text
+        assert "libcurl" in text
+        assert "/tmp/scripts/api_client.c" in text
 
 
 class TestEngineerTemplates: