fix: accept custom_body in URL-based create_pass_through_route endpoint_func

[joereyna]

Summary

• create_pass_through_route has two endpoint_func implementations: one for adapter-based targets and one for URL-based targets
• The adapter-based endpoint_func correctly accepts custom_body in its signature
• The URL-based endpoint_func (the except branch) was missing custom_body, causing a TypeError when callers like bedrock_proxy_route pass custom_body=data
• Fix: add custom_body: Optional[dict] = None to the URL-based endpoint_func signature and give it precedence over the request-parsed body

Test plan

• test (proxy-misc) — test_create_pass_through_route_custom_body_url_target passes

[vercel]

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Project	Deployment	Actions	Updated (UTC)
litellm	Error		Mar 12, 2026 2:13am

[greptile-apps]

Greptile Summary

This PR fixes a TypeError: endpoint_func() got an unexpected keyword argument 'custom_body' that occurred when bedrock_proxy_route (and similar callers) called the URL-based endpoint_func returned by create_pass_through_route with custom_body=data. The adapter-based endpoint_func already accepted this parameter; the URL-based one (the except branch) was missing it.

Key changes:

• Added custom_body: Optional[dict] = None to the URL-based endpoint_func signature, matching the adapter-based one.
• Implemented a simple precedence rule: if the caller supplies custom_body, it is used directly; otherwise, the body parsed from the raw request (custom_body_data) is used as a fallback, preserving existing behavior.
• The accompanying mock tests (test_create_pass_through_route_custom_body_url_target and test_create_pass_through_route_no_custom_body_falls_back) were already merged into main via PR fix: add custom_body parameter to endpoint_func in create_pass_through_route #20849 and cover both the new precedence path and the fallback path.

Note: This is a re-application of the identical fix from PR #20849 (ab4b6197e), which appears to have been lost from the base branch of this PR due to a divergent merge history.

Confidence Score: 5/5

• This PR is safe to merge — it is a minimal, targeted bug fix with no backward-incompatible changes and full mock test coverage.
• The change is a two-line addition (parameter + precedence branch) that strictly extends the existing signature, does not alter the fallback path, and directly mirrors the already-working adapter-based implementation. The existing test suite in main already validates both the new and the fallback behavior.
• No files require special attention.

Important Files Changed

Filename	Overview
litellm/proxy/pass_through_endpoints/pass_through_endpoints.py	Adds custom_body: Optional[dict] = None to the URL-based endpoint_func in create_pass_through_route, with correct precedence over request-parsed body; fixes the TypeError raised when bedrock_proxy_route passes custom_body=data.

Sequence Diagram

sequenceDiagram
    participant Client
    participant bedrock_proxy_route
    participant create_pass_through_route
    participant endpoint_func (URL-based)
    participant _parse_request_data_by_content_type
    participant pass_through_request

    Client->>bedrock_proxy_route: POST /bedrock/{endpoint}
    bedrock_proxy_route->>bedrock_proxy_route: data = await request.json()
    bedrock_proxy_route->>bedrock_proxy_route: SigV4-sign request body
    bedrock_proxy_route->>create_pass_through_route: create_pass_through_route(endpoint, target, ...)
    create_pass_through_route-->>bedrock_proxy_route: endpoint_func (URL-based)
    bedrock_proxy_route->>endpoint_func (URL-based): await endpoint_func(..., custom_body=data)
    Note over endpoint_func (URL-based): custom_body param now accepted ✅ (was TypeError before fix)
    endpoint_func (URL-based)->>_parse_request_data_by_content_type: parse request (for query_params, etc.)
    _parse_request_data_by_content_type-->>endpoint_func (URL-based): query_params_data, custom_body_data, ...
    Note over endpoint_func (URL-based): custom_body != None → use caller-supplied body (takes precedence)
    endpoint_func (URL-based)->>pass_through_request: pass_through_request(..., custom_body=data)
    pass_through_request-->>Client: Forwarded response

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_{Last reviewed commit: 8392967}