Add runtime environment variable overrides for provider configuration

SETUP.md

@@ -0,0 +1,234 @@
+# Setup Guide - Codex with Runtime Provider Overrides
+
+This fork adds environment variable support for overriding provider configuration at runtime.
+
+## Prerequisites
+
+- **Rust toolchain** (1.70 or newer)
+- **Node.js** 16+ (for the CLI wrapper)
+- **Git**
+
+Install Rust if needed:
+```bash
+curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+source "$HOME/.cargo/env"
+```
+
+## Installation Steps
+
+### 1. Clone the Fork
+
+```bash
+git clone https://github.com/daniel-salib/codex.git
+cd codex
+git checkout runtime-provider-overrides
+```
+
+Or if you already have it cloned:
+```bash
+cd /path/to/codex
+git fetch origin
+git checkout runtime-provider-overrides
+git pull
+```
+
+### 2. Build the Rust Binary
+
+```bash
+cd codex-rs
+cargo build --release
+# Or if behind a corporate proxy:
+# with-proxy cargo build --release
+```
+
+This will take several minutes on first build. The binary will be at:
+`codex-rs/target/release/codex`
+
+### 3. Install to Vendor Directory
+
+Copy the compiled binary to where the CLI wrapper expects it:
+
+```bash
+# From the codex root directory
+mkdir -p codex-cli/vendor/x86_64-unknown-linux-musl/codex
+cp codex-rs/target/release/codex codex-cli/vendor/x86_64-unknown-linux-musl/codex/codex
+chmod +x codex-cli/vendor/x86_64-unknown-linux-musl/codex/codex
+```
+
+### 4. Make CLI Wrapper Executable
+
+The Node.js wrapper needs execute permissions:
+
+```bash
+# From the codex root directory
+chmod +x codex-cli/bin/codex.js
+```
+
+### 5. Install Globally (Choose One Method)
+
+#### Option A: Symlink (Recommended for Development)
+
+```bash
+# Make sure ~/bin exists and is in your PATH
+mkdir -p ~/bin
+
+# Create symlink
+ln -sf "$(pwd)/codex-cli/bin/codex.js" ~/bin/codex
+
+# Add to PATH if needed (add to ~/.bashrc or ~/.zshrc)
+export PATH="$HOME/bin:$PATH"
+```
+
+### 6. Verify Installation
+
+Test that codex is working:
+
+```bash
+codex --version
+# Should output: codex-cli 0.0.0
+```
+
+If you get a "Permission denied" error, make sure you completed Step 4 (making codex.js executable).
+
+### 7. Configure Codex for Local vLLM
+
+Create a codex config file that defines a vLLM provider:
+
+```bash
+mkdir -p ~/.codex
+
+cat > ~/.codex/config.toml << 'EOF'
+# Default model name - vLLM typically exposes models as "default"
+model = "default"
+
+# Default provider to use
+model_provider = "vllm-local"
+
+[model_providers.vllm-local]
+name = "Local vLLM"
+# Fallback values - these can be overridden by environment variables (see next step)
+base_url = "http://localhost:8000/v1"
+wire_api = "responses"
+env_key = "OPENAI_API_KEY"
+EOF
+```
+
+### 8. Set Up Environment Variables
+
+If you want to easily switch between different vLLM servers without editing config files:
+
+```bash
+# Add to ~/.bashrc or ~/.zshrc
+export OPENAI_API_KEY="dummy-key-for-local-vllm"
+
+# Runtime provider overrides - these override config.toml values!
+export CODEX_PROVIDER_VLLM_LOCAL_BASE_URL="http://localhost:8000/v1"
+export CODEX_PROVIDER_VLLM_LOCAL_WIRE_API="responses"
+
+export PATH="$HOME/bin:$PATH"
+```
+
+Then reload your shell config:
+
+```bash
+source ~/.bashrc  # or source ~/.zshrc
+```
+
+### 9. Test Your Setup
+
+Make sure your vLLM server is running on port 8000, then test codex:
+
+```bash
+# Simple test
+codex exec --dangerously-bypass-approvals-and-sandbox "what's 2+2?"
+
+# You should see output like:
+# --------
+# workdir: /your/current/directory
+# model: default
+# provider: vllm-local
+# approval: never
+# sandbox: danger-full-access
+# --------
+```
+
+### 10. Changing vLLM Server Ports (Optional)
+
+**If you used Option A (Simple Setup):**
+
+Edit your config file to change the port:
+```bash
+nano ~/.codex/config.toml
+# Change: base_url = "http://localhost:9000/v1"
+```
+
+**If you used Option B (Runtime Overrides):**
+
+Just update the environment variable (no config file editing needed!):
+```bash
+export CODEX_PROVIDER_VLLM_LOCAL_BASE_URL="http://localhost:9000/v1"
+# That's it! This demonstrates the power of runtime overrides.
+```
+
+## Usage
+
+### Environment Variable Overrides (This Fork's Feature)
+
+This fork allows you to override provider settings via environment variables **without modifying config files**:
+
+```bash
+# Format: CODEX_PROVIDER_<PROVIDER_ID>_BASE_URL and CODEX_PROVIDER_<PROVIDER_ID>_WIRE_API
+# The PROVIDER_ID is the kebab-case provider name converted to SCREAMING_SNAKE_CASE
+# Example: "vllm-local" becomes "VLLM_LOCAL"
+
+export CODEX_PROVIDER_VLLM_LOCAL_BASE_URL="http://localhost:8000/v1"
+export CODEX_PROVIDER_VLLM_LOCAL_WIRE_API="responses"
+
+# Now any codex command automatically uses these overrides
+codex exec --dangerously-bypass-approvals-and-sandbox "your prompt here"
+```
+
+**Benefits:**
+- Change provider URL without editing config files
+- Switch between different vLLM servers easily
+- Great for testing and development
+
+**Note:** The provider must already exist in your `~/.codex/config.toml`. These environment variables only override the `base_url` and `wire_api` fields.
+
+### Alternative: Config Overrides with -c Flag
+
+You can also override settings directly on the command line (works with any codex version):
+
+```bash
+# Override specific fields (must be on one line, no line breaks in the TOML)
+codex exec -c "model_providers.vllm-local.base_url=http://localhost:9000/v1" -c "model_providers.vllm-local.wire_api=responses" --dangerously-bypass-approvals-and-sandbox "what's 2+2?"
+
+# Or define a completely new provider inline (all on one line!)
+codex exec -c "model_providers.my-vllm={ name = 'My vLLM', base_url = 'http://localhost:8000/v1', wire_api = 'responses', env_key = 'OPENAI_API_KEY' }" -c model_provider="my-vllm" -c model="default" --dangerously-bypass-approvals-and-sandbox "what's 2+2?"
+```
+
+**Important:** When using `-c` with inline TOML tables (`{ ... }`), the entire command must be on **one line** with no line breaks inside the TOML string, or the parser will fail.
+
+## Troubleshooting
+
+### Error: "Missing environment variable: OPENAI_API_KEY"
+Set a dummy value:
+```bash
+export OPENAI_API_KEY="dummy-key-for-local-vllm"
+```
+
+### Error: "The model `gpt-5-codex` does not exist"
+Update your config to use the correct model name (usually "default" for vLLM):
+```bash
+# Add to ~/.codex/config.toml
+model = "default"
+```
+
+### Error: "unexpected status 404 Not Found"
+Check that your vLLM server is running and accessible:
+```bash
+curl http://localhost:8000/v1/models
+```
+
+### Error: "invalid type: string ... expected struct ModelProviderInfo"
+You have line breaks in your `-c` TOML inline table. Put the entire command on one line.

codex-rs/core/src/config/mod.rs

@@ -279,6 +279,75 @@ pub struct Config {
     pub otel: crate::config::types::OtelConfig,
 }
 
+/// Apply environment variable overrides to a model provider configuration.
+///
+/// This function checks for provider-specific environment variables that can
+/// override the base_url and wire_api settings at runtime without modifying
+/// config files. The environment variables follow this pattern:
+///
+/// - `CODEX_PROVIDER_<PROVIDER_ID>_BASE_URL` - Override the base URL
+/// - `CODEX_PROVIDER_<PROVIDER_ID>_WIRE_API` - Override the wire API ("chat" or "responses")
+///
+/// Where `<PROVIDER_ID>` is the uppercased provider ID with hyphens converted to underscores.
+/// For example, for provider "vllm-local":
+/// - `CODEX_PROVIDER_VLLM_LOCAL_BASE_URL`
+/// - `CODEX_PROVIDER_VLLM_LOCAL_WIRE_API`
+fn apply_provider_env_overrides(provider: &mut ModelProviderInfo, provider_id: &str) {
+    use crate::model_provider_info::WireApi;
+
+    // Convert provider ID to environment variable suffix
+    // e.g., "vllm-local" -> "VLLM_LOCAL"
+    let provider_suffix = provider_id.to_uppercase().replace('-', "_");
+
+    // Check for base URL override
+    let base_url_env = format!("CODEX_PROVIDER_{}_BASE_URL", provider_suffix);
+    if let Ok(base_url) = std::env::var(&base_url_env) {
+        let trimmed = base_url.trim();
+        if !trimmed.is_empty() {
+            tracing::info!(
+                "Overriding provider '{}' base_url from environment variable {}: {}",
+                provider_id,
+                base_url_env,
+                trimmed
+            );
+            provider.base_url = Some(trimmed.to_string());
+        }
+    }
+
+    // Check for wire API override
+    let wire_api_env = format!("CODEX_PROVIDER_{}_WIRE_API", provider_suffix);
+    if let Ok(wire_api_str) = std::env::var(&wire_api_env) {
+        let trimmed = wire_api_str.trim().to_lowercase();
+        if !trimmed.is_empty() {
+            match trimmed.as_str() {
+                "responses" => {
+                    tracing::info!(
+                        "Overriding provider '{}' wire_api from environment variable {}: responses",
+                        provider_id,
+                        wire_api_env
+                    );
+                    provider.wire_api = WireApi::Responses;
+                }
+                "chat" => {
+                    tracing::info!(
+                        "Overriding provider '{}' wire_api from environment variable {}: chat",
+                        provider_id,
+                        wire_api_env
+                    );
+                    provider.wire_api = WireApi::Chat;
+                }
+                _ => {
+                    tracing::warn!(
+                        "Invalid value for {}: '{}' (expected 'chat' or 'responses')",
+                        wire_api_env,
+                        trimmed
+                    );
+                }
+            }
+        }
+    }
+}
+
 impl Config {
     pub async fn load_with_cli_overrides(
         cli_overrides: Vec<(String, TomlValue)>,
@@ -1070,7 +1139,7 @@ impl Config {
             .or(config_profile.model_provider)
             .or(cfg.model_provider)
             .unwrap_or_else(|| "openai".to_string());
-        let model_provider = model_providers
+        let mut model_provider = model_providers
             .get(&model_provider_id)
             .ok_or_else(|| {
                 std::io::Error::new(
@@ -1080,6 +1149,10 @@ impl Config {
             })?
             .clone();
 
+        // Apply environment variable overrides for provider configuration
+        // This allows runtime override of base_url and wire_api without modifying config files
+        apply_provider_env_overrides(&mut model_provider, &model_provider_id);
+
         let shell_environment_policy = cfg.shell_environment_policy.into();
 
         let history = cfg.history.unwrap_or_default();