feat: Allow emscripten users to define HTTP handler by cdmurph32 · Pull Request #1936 · contentauth/c2pa-rs

cdmurph32 · 2026-03-16T15:17:35Z

Changes in this pull request

Follow-up to the Emscripten build support added in c2pa-rs.

Emscripten does not support reqwest or ureq, the standard http handlers in the Rust SDK. The Rust SDK supports users defining their own http handlers through the context. We need to expose this in the C Bindings.

Checklist

This PR represents a single feature, fix, or change.
All applicable changes have been documented.
Any TO DO items (or similar) have been entered as GitHub issues and the link to that issue has been included in a comment.

codecov · 2026-03-16T15:23:52Z

Codecov Report

❌ Patch coverage is 0% with 83 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.72%. Comparing base (b6d4ebc) to head (c7e8396).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
c2pa_c_ffi/src/c_api.rs	0.00%	83 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1936      +/-   ##
==========================================
+ Coverage   76.50%   76.72%   +0.21%     
==========================================
  Files         172      175       +3     
  Lines       41142    42254    +1112     
==========================================
+ Hits        31475    32418     +943     
- Misses       9667     9836     +169

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codspeed-hq · 2026-03-16T15:25:30Z

Merging this PR will not alter performance

✅ 16 untouched benchmarks
⏩ 2 skipped benchmarks¹

_{Comparing expose_custom_http_handler_c_api (c7e8396) with main (0e37237)}

2 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

c2pa_c_ffi/src/c_api.rs

ok-nick · 2026-03-18T17:29:12Z

c2pa_c_ffi/examples/emscripten_example.cpp

Do we want to add a cpp examples in this repo? This feels more like a c2pa-c example? (cc @gpeacock)

It seems like we might also be able to reuse a lot of structs defined there.

c2pa_c_ffi/src/c_api.rs

ok-nick · 2026-03-19T17:46:39Z

c2pa_c_ffi/src/c_api.rs

+
+        use c2pa::http::HttpResolverError;
+
+        let uri_cstr = CString::new(request.uri().to_string())


Not a blocker here, but it would be clean if impl TryFrom<Request> for C2paHttpRequest and same for response.

I'll give it a shot.

ok-nick · 2026-03-19T17:48:37Z

c2pa_c_ffi/src/c_api.rs

+        let response_body = if c_response.body.is_null() || c_response.body_len == 0 {
+            Vec::new()
+        } else {
+            unsafe { std::slice::from_raw_parts(c_response.body, c_response.body_len).to_vec() }
+        };
+
+        // Release the callback-owned buffer.
+        if let Some(free_fn) = c_response.body_free {
+            if !c_response.body.is_null() {
+                unsafe { free_fn(c_response.body) };
+            }
+        }
+
+        if rc != 0 {
+            let msg = CimplError::last_message()
+                .unwrap_or_else(|| "HTTP callback returned error".to_string());
+            return Err(HttpResolverError::Other(msg.into()));
+        }
+
+        let response = c2pa::http::http::Response::builder()
+            .status(c_response.status as u16)
+            .body(Box::new(std::io::Cursor::new(response_body)) as Box<dyn std::io::Read>)
+            .map_err(HttpResolverError::Http)?;
+        Ok(response)
+    }


Would it be possible to return a Cursor over c_response.body rather than cloning it into a vec? We can free it through impl Drop for C2paHttpResponse.

* use libc::free instead of custom deallocator * impl TryFrom<Request/Response>

ok-nick

Nice work, looks great. Approving with the exception that we consider where the C++ example belongs.

ok-nick · 2026-03-23T16:49:29Z

c2pa_c_ffi/src/c_api.rs

+    ///
+    /// # Safety
+    /// `self.body` must have been allocated with `malloc()` (or be null).
+    unsafe fn into_http_response(


Can also implement TryFrom here too.

ok-nick · 2026-03-23T16:50:04Z

c2pa_c_ffi/src/c_api.rs

+///
+/// Use [`as_ffi`](OwnedC2paHttpRequest::as_ffi) to obtain the `#[repr(C)]` view
+/// whose pointers borrow from this struct.
+struct OwnedC2paHttpRequest {


How come you split OwnedC2paHttpRequest and C2paHttpRequest into separate structs?

C2paHttpRequest needs *const c_char fields so that cbindgen can generate the bindings.
OwnedC2paHttpRequest owns the CString data (Box<[u8]>).

ok-nick · 2026-03-23T16:53:08Z

c2pa_c_ffi/examples/emscripten_example.cpp

It seems like we might also be able to reuse a lot of structs defined there.

cdmurph32 force-pushed the expose_custom_http_handler_c_api branch from 7f658f3 to bafb849 Compare March 16, 2026 15:56

cdmurph32 added the check-release Add this label to any PR to invoke a larger suite of tests. label Mar 17, 2026

cdmurph32 marked this pull request as ready for review March 17, 2026 17:00

ok-nick reviewed Mar 18, 2026

View reviewed changes

ok-nick reviewed Mar 19, 2026

View reviewed changes

cdmurph32 added 7 commits March 23, 2026 09:19

feat: Allow emscripten users to define HTTP handler

2e4fd6a

feat: allow non-wasm targets to use http resolver

59feee1

docs: Pare down emscripten docs

88d2c76

fix: clippy

36ebaf1

fix: Request/Response structs like the Rust SDK

1a7db77

docs: docs fix

471f600

fix: comment incorporation

22317c4

* use libc::free instead of custom deallocator * impl TryFrom<Request/Response>

cdmurph32 force-pushed the expose_custom_http_handler_c_api branch from 5155fbe to 22317c4 Compare March 23, 2026 13:19

chore: update rustls-webpki for security fix

a7b24b6

ok-nick approved these changes Mar 23, 2026

View reviewed changes

feat: Implement TryFrom for C2paHttpResponse

c7e8396


		use c2pa::http::HttpResolverError;

		let uri_cstr = CString::new(request.uri().to_string())

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cdmurph32 commented Mar 16, 2026

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Merging this PR will not alter performance

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codecov bot commented Mar 16, 2026 •

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