fix: Replace TextReceiveStream with raw byte stream reading

Fixes #32 - JSON parsing fails for large tool results

The anyio.TextReceiveStream has issues when reading large lines (>10KB)
containing UTF-8 characters, causing JSON parsing to fail at position 130.

This fix:
- Removes dependency on TextReceiveStream
- Reads stdout/stderr as raw byte streams
- Manually handles line buffering and UTF-8 decoding
- Properly processes remaining buffer content

The issue occurred because TextReceiveStream appears to have a bug when
handling large lines with specific content patterns, particularly those
containing UTF-8 characters like the arrow symbol (→) used in line numbers.

Tested with:
- Large file reads (>30KB)
- Files containing UTF-8 characters
- Multiple concurrent tool uses

src/claude_code_sdk/_internal/transport/subprocess_cli.py

@@ -10,7 +10,6 @@ from typing import Any
 
 import anyio
 from anyio.abc import Process
-from anyio.streams.text import TextReceiveStream
 
 from ..._errors import CLIConnectionError, CLINotFoundError, ProcessError
 from ..._errors import CLIJSONDecodeError as SDKJSONDecodeError
@@ -32,8 +31,8 @@ class SubprocessCLITransport(Transport):
         self._cli_path = str(cli_path) if cli_path else self._find_cli()
         self._cwd = str(options.cwd) if options.cwd else None
         self._process: Process | None = None
-        self._stdout_stream: TextReceiveStream | None = None
+        self._stdout_stream: Any | None = None  # Raw stdout stream
-        self._stderr_stream: TextReceiveStream | None = None
+        self._stderr_stream: Any | None = None  # Raw stderr stream
 
     def _find_cli(self) -> str:
         """Find Claude Code CLI binary."""
@@ -131,9 +130,11 @@ class SubprocessCLITransport(Transport):
             )
 
             if self._process.stdout:
-                self._stdout_stream = TextReceiveStream(self._process.stdout)
+                # Use raw stream to avoid TextReceiveStream issues with large JSON
+                self._stdout_stream = self._process.stdout
             if self._process.stderr:
-                self._stderr_stream = TextReceiveStream(self._process.stderr)
+                # Use raw stream for stderr as well
+                self._stderr_stream = self._process.stderr
 
         except FileNotFoundError as e:
             raise CLINotFoundError(f"Claude Code not found at: {self._cli_path}") from e
@@ -174,8 +175,13 @@ class SubprocessCLITransport(Transport):
             """Read stderr in background."""
             if self._stderr_stream:
                 try:
-                    async for line in self._stderr_stream:
+                    # Read as bytes and decode
-                        stderr_lines.append(line.strip())
+                    buffer = b""
+                    async for chunk in self._stderr_stream:
+                        buffer += chunk
+                        while b'\n' in buffer:
+                            line, buffer = buffer.split(b'\n', 1)
+                            stderr_lines.append(line.decode('utf-8', errors='replace').strip())
                 except anyio.ClosedResourceError:
                     pass
 
@@ -183,22 +189,41 @@ class SubprocessCLITransport(Transport):
             tg.start_soon(read_stderr)
 
             try:
-                async for line in self._stdout_stream:
+                # Read stdout as bytes to properly handle large JSON lines
-                    line_str = line.strip()
+                buffer = b""
-                    if not line_str:
+                async for chunk in self._stdout_stream:
-                        continue
+                    buffer += chunk
+                    
+                    # Process complete lines
+                    while b'\n' in buffer:
+                        line_bytes, buffer = buffer.split(b'\n', 1)
+                        line_str = line_bytes.decode('utf-8', errors='replace').strip()
+                        
+                        if not line_str:
+                            continue
 
-                    try:
-                        data = json.loads(line_str)
                         try:
+                            data = json.loads(line_str)
+                            try:
+                                yield data
+                            except GeneratorExit:
+                                # Handle generator cleanup gracefully
+                                return
+                        except json.JSONDecodeError as e:
+                            if line_str.startswith("{") or line_str.startswith("["):
+                                raise SDKJSONDecodeError(line_str, e) from e
+                            continue
+
+                # Process any remaining data in buffer
+                if buffer:
+                    line_str = buffer.decode('utf-8', errors='replace').strip()
+                    if line_str:
+                        try:
+                            data = json.loads(line_str)
                             yield data
-                        except GeneratorExit:
+                        except json.JSONDecodeError:
-                            # Handle generator cleanup gracefully
+                            # Incomplete JSON at end, ignore
-                            return
+                            pass
-                    except json.JSONDecodeError as e:
-                        if line_str.startswith("{") or line_str.startswith("["):
-                            raise SDKJSONDecodeError(line_str, e) from e
-                        continue
 
             except anyio.ClosedResourceError:
                 pass

src/claude_code_sdk/_internal/transport/subprocess_cli_fixed.py

@@ -0,0 +1,240 @@
+"""Subprocess transport implementation using Claude Code CLI with fix for large JSON messages."""
+
+import json
+import os
+import shutil
+from collections.abc import AsyncIterator
+from pathlib import Path
+from subprocess import PIPE
+from typing import Any
+
+import anyio
+from anyio.abc import Process
+
+from ..._errors import CLIConnectionError, CLINotFoundError, ProcessError
+from ..._errors import CLIJSONDecodeError as SDKJSONDecodeError
+from ...types import ClaudeCodeOptions
+from . import Transport
+
+
+class SubprocessCLITransport(Transport):
+    """Subprocess transport using Claude Code CLI."""
+
+    def __init__(
+        self,
+        prompt: str,
+        options: ClaudeCodeOptions,
+        cli_path: str | Path | None = None,
+    ):
+        self._prompt = prompt
+        self._options = options
+        self._cli_path = str(cli_path) if cli_path else self._find_cli()
+        self._cwd = str(options.cwd) if options.cwd else None
+        self._process: Process | None = None
+        self._stdout: Any = None  # Store raw stdout
+        self._stderr: Any = None  # Store raw stderr
+
+    def _find_cli(self) -> str:
+        """Find Claude Code CLI binary."""
+        if cli := shutil.which("claude"):
+            return cli
+
+        locations = [
+            Path.home() / ".npm-global/bin/claude",
+            Path("/usr/local/bin/claude"),
+            Path.home() / ".local/bin/claude",
+            Path.home() / "node_modules/.bin/claude",
+            Path.home() / ".yarn/bin/claude",
+        ]
+
+        for path in locations:
+            if path.exists() and path.is_file():
+                return str(path)
+
+        node_installed = shutil.which("node") is not None
+
+        if not node_installed:
+            error_msg = "Claude Code requires Node.js, which is not installed.\n\n"
+            error_msg += "Install Node.js from: https://nodejs.org/\n"
+            error_msg += "\nAfter installing Node.js, install Claude Code:\n"
+            error_msg += "  npm install -g @anthropic-ai/claude-code"
+            raise CLINotFoundError(error_msg)
+
+        raise CLINotFoundError(
+            "Claude Code not found. Install with:\n"
+            "  npm install -g @anthropic-ai/claude-code\n"
+            "\nIf already installed locally, try:\n"
+            '  export PATH="$HOME/node_modules/.bin:$PATH"\n'
+            "\nOr specify the path when creating transport:\n"
+            "  SubprocessCLITransport(..., cli_path='/path/to/claude')"
+        )
+
+    def _build_command(self) -> list[str]:
+        """Build CLI command with arguments."""
+        cmd = [self._cli_path, "--output-format", "stream-json", "--verbose"]
+
+        if self._options.system_prompt:
+            cmd.extend(["--system-prompt", self._options.system_prompt])
+
+        if self._options.append_system_prompt:
+            cmd.extend(["--append-system-prompt", self._options.append_system_prompt])
+
+        if self._options.allowed_tools:
+            cmd.extend(["--allowedTools", ",".join(self._options.allowed_tools)])
+
+        if self._options.max_turns:
+            cmd.extend(["--max-turns", str(self._options.max_turns)])
+
+        if self._options.disallowed_tools:
+            cmd.extend(["--disallowedTools", ",".join(self._options.disallowed_tools)])
+
+        if self._options.model:
+            cmd.extend(["--model", self._options.model])
+
+        if self._options.permission_prompt_tool_name:
+            cmd.extend(
+                ["--permission-prompt-tool", self._options.permission_prompt_tool_name]
+            )
+
+        if self._options.permission_mode:
+            cmd.extend(["--permission-mode", self._options.permission_mode])
+
+        if self._options.continue_conversation:
+            cmd.append("--continue")
+
+        if self._options.resume:
+            cmd.extend(["--resume", self._options.resume])
+
+        if self._options.mcp_servers:
+            cmd.extend(
+                ["--mcp-config", json.dumps({"mcpServers": self._options.mcp_servers})]
+            )
+
+        cmd.extend(["--print", self._prompt])
+        return cmd
+
+    async def connect(self) -> None:
+        """Start subprocess."""
+        if self._process:
+            return
+
+        cmd = self._build_command()
+        try:
+            self._process = await anyio.open_process(
+                cmd,
+                stdin=None,
+                stdout=PIPE,
+                stderr=PIPE,
+                cwd=self._cwd,
+                env={**os.environ, "CLAUDE_CODE_ENTRYPOINT": "sdk-py"},
+            )
+
+            # Store raw streams instead of wrapping in TextReceiveStream
+            self._stdout = self._process.stdout
+            self._stderr = self._process.stderr
+
+        except FileNotFoundError as e:
+            raise CLINotFoundError(f"Claude Code not found at: {self._cli_path}") from e
+        except Exception as e:
+            raise CLIConnectionError(f"Failed to start Claude Code: {e}") from e
+
+    async def disconnect(self) -> None:
+        """Terminate subprocess."""
+        if not self._process:
+            return
+
+        if self._process.returncode is None:
+            try:
+                self._process.terminate()
+                with anyio.fail_after(5.0):
+                    await self._process.wait()
+            except TimeoutError:
+                self._process.kill()
+                await self._process.wait()
+            except ProcessLookupError:
+                pass
+
+        self._process = None
+        self._stdout = None
+        self._stderr = None
+
+    async def send_request(self, messages: list[Any], options: dict[str, Any]) -> None:
+        """Not used for CLI transport - args passed via command line."""
+
+    async def receive_messages(self) -> AsyncIterator[dict[str, Any]]:
+        """Receive messages from CLI with proper handling of large JSON lines."""
+        if not self._process or not self._stdout:
+            raise CLIConnectionError("Not connected")
+
+        stderr_lines = []
+
+        async def read_stderr() -> None:
+            """Read stderr in background."""
+            if self._stderr:
+                try:
+                    # Read stderr as bytes and decode
+                    buffer = b""
+                    async for chunk in self._stderr:
+                        buffer += chunk
+                        while b'\n' in buffer:
+                            line, buffer = buffer.split(b'\n', 1)
+                            stderr_lines.append(line.decode('utf-8', errors='replace').strip())
+                except anyio.ClosedResourceError:
+                    pass
+
+        async with anyio.create_task_group() as tg:
+            tg.start_soon(read_stderr)
+
+            try:
+                # Read stdout as bytes to avoid TextReceiveStream issues
+                buffer = b""
+                async for chunk in self._stdout:
+                    buffer += chunk
+                    
+                    # Process complete lines
+                    while b'\n' in buffer:
+                        line_bytes, buffer = buffer.split(b'\n', 1)
+                        line_str = line_bytes.decode('utf-8', errors='replace').strip()
+                        
+                        if not line_str:
+                            continue
+
+                        try:
+                            data = json.loads(line_str)
+                            try:
+                                yield data
+                            except GeneratorExit:
+                                # Handle generator cleanup gracefully
+                                return
+                        except json.JSONDecodeError as e:
+                            if line_str.startswith("{") or line_str.startswith("["):
+                                raise SDKJSONDecodeError(line_str, e) from e
+                            continue
+
+                # Process any remaining data in buffer
+                if buffer:
+                    line_str = buffer.decode('utf-8', errors='replace').strip()
+                    if line_str:
+                        try:
+                            data = json.loads(line_str)
+                            yield data
+                        except json.JSONDecodeError:
+                            # Incomplete JSON at end, ignore
+                            pass
+
+            except anyio.ClosedResourceError:
+                pass
+
+        await self._process.wait()
+        if self._process.returncode is not None and self._process.returncode != 0:
+            stderr_output = "\n".join(stderr_lines)
+            if stderr_output and "error" in stderr_output.lower():
+                raise ProcessError(
+                    "CLI process failed",
+                    exit_code=self._process.returncode,
+                    stderr=stderr_output,
+                )
+
+    def is_connected(self) -> bool:
+        """Check if subprocess is running."""
+        return self._process is not None and self._process.returncode is None