Forward a data: URIContent to Anthropic as an inline base64 block by PratikDhanave · Pull Request #939 · microsoft/agent-framework-go

PratikDhanave (PratikDhanave) · 2026-08-28T08:41:07Z

Problem

In provider/anthropicprovider/agent.go, buildMessageParam's *message.URIContent case handles image and PDF only as URL sources (anthropic.URLImageSourceParam / URLPDFSourceParam), which require an external http(s) reference. A URIContent carrying a data: URI is sent with the entire data:image/png;base64,... string as the url, which Anthropic rejects (400 invalid image source). The identical payload as DataContent succeeds — a cross-provider and intra-file inconsistency.

Fix

Detect a data: URI, decode it with message.DecodeDataURI, and emit an inline base64 image/PDF block using the same primitives as the DataContent branch (anthropic.NewImageBlockBase64 / anthropic.Base64PDFSourceParam). Non-data: http(s) URLs keep the URL source.

This mirrors the sibling providers that already special-case data: URIs on URIContent: Gemini (data: → InlineData) and OpenAI chat (data: → inline DataContent mapping).

Test

TestBuildMessageParam_DataURIImageForwardedAsBase64 sends a URIContent with a data:image/png;base64,... URI and asserts the outgoing content block is a base64 image source. Fails before the fix (source.type == "url" with the data URI), passes after.

buildMessageParam's URIContent case only handled image and PDF as URL sources (anthropic.URLImageSourceParam / URLPDFSourceParam), which require an external http(s) reference. A URIContent carrying a data: URI was sent with the whole data: string as the url, which Anthropic rejects (400). Decode the data: URI and emit a base64 image/PDF block instead, reusing the same primitives as the DataContent branch (NewImageBlockBase64 / Base64PDFSourceParam). This mirrors the Gemini provider (data: -> InlineData) and the OpenAI chat provider (data: -> inline), which already special-case data: URIs on URIContent. Non-data http(s) URLs keep the URL source.

Copilot

Pull request overview

Fixes Anthropic provider handling of message.URIContent that contains data: URIs by converting them into inline base64 image/PDF blocks (instead of incorrectly sending the full data: URI as a URL source, which Anthropic rejects).

Changes:

Detect data: URIs in buildMessageParam and map them to Anthropic base64 image/PDF content blocks.
Add a regression test asserting data:-URI URIContent images are forwarded as base64 sources.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
provider/anthropicprovider/agent.go	Adds `data:` URI detection/decoding and forwards inline content as base64 blocks for Anthropic.
provider/anthropicprovider/agent_test.go	Adds a regression test for `data:` URI image forwarding behavior.

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PratikDhanave (PratikDhanave) · 2026-09-06T03:24:30Z

+			case strings.HasPrefix(strings.ToLower(c.URI), "data:"):
+				// A data: URI carries the bytes inline. Anthropic's URL image/PDF
+				// sources require an external http(s) reference, so a data: URI sent
+				// as a url source is rejected; decode it and send a base64 block
+				// instead, mirroring the DataContent branch and the Gemini/OpenAI
+				// data: handling.
+				data, mediaType, err := message.DecodeDataURI(c.URI)
+				if err != nil {
+					break
+				}
+				encoded := base64.StdEncoding.EncodeToString(data)
+				switch {
+				case strings.HasPrefix(mediaType, "image/"):
+					content = append(content, anthropic.NewImageBlockBase64(mediaType, encoded))
+				case isPDFMediaType(mediaType):
+					content = append(content, anthropic.NewDocumentBlock(anthropic.Base64PDFSourceParam{Data: encoded}))
+				}


Fixed — a DecodeDataURI failure now returns an explicit error (anthropicprovider: failed to decode data URI content) instead of break-ing and dropping the content, matching geminiprovider. Also added the URIContent.MediaType override and case-insensitive media-type matching.

PratikDhanave (PratikDhanave) · 2026-09-06T03:24:32Z

+		for _, b := range blocks {
+			block, _ := b.(map[string]any)
+			source, _ := block["source"].(map[string]any)
+			if block["type"] == "image" && source["type"] == "base64" && source["media_type"] == "image/png" {


Strengthened the test to assert the forwarded base64 payload (source["data"] == "aGVsbG8="), so it would now fail if the wrong bytes were encoded/forwarded.

Quim Muntal (qmuntal) · 2026-08-28T14:07:55Z

Fix codereview comments.

Quim Muntal (qmuntal)

Fix codereview findings.

- Return an explicit error (matching geminiprovider) instead of swallowing a DecodeDataURI failure with break, which would drop the content and send a request with missing blocks. - Let an explicit URIContent.MediaType override the media type parsed from the data: URI, and match media types case-insensitively (mirrors gemini). - Strengthen the test to assert the forwarded base64 payload, not just the source type/media_type.

github-actions · 2026-09-06T03:30:05Z

Scope: internal-only (bugfix), no exported Go API change

Changed Go contract: None. buildMessageParam in provider/anthropicprovider/agent.go (unexported) gains a (redacted) URI branch in the *message.URIContentcase that decodes inline base64 content via the existingmessage.DecodeDataURIhelper and emitsanthropic.NewImageBlockBase64/anthropic.Base64PDFSourceParam, instead of passing the raw data URI string as a URLImageSourceParam/URLPDFSourceParam (which Anthropic rejects). No new exported functions, types, or options; the added test (TestBuildMessageParam_DataURIImageForwardedAsBase64) only exercises existing behavior via Run`.

Upstream evidence reviewed: This PR does not introduce a Go-only public feature or diverge from .NET/Python — it fixes a Go-internal cross-provider inconsistency. Within the Go repo itself, provider/openaiprovider/chat.go:695 (strings.HasPrefix(strings.ToLower(uri), "(redacted) already special-cases (redacted) URIs for URIContent, and the PR description states the Gemini provider does the same ((redacted) → InlineData`), so the fix brings Anthropic in line with the other two Go providers' existing observable behavior. No corresponding upstream .NET/Python file was needed since this doesn't add or change any capability beyond what Go's own OpenAI/Gemini providers already do — it only corrects a bug where Anthropic diverged from the rest of the Go implementation.

Result: aligned. This is a targeted bugfix that removes an intra-repo inconsistency (Anthropic previously mishandled (redacted) URIContent while OpenAI/Gemini providers already handled it correctly and DataContent succeeded with identical bytes). No public API surface changed, so public-api-changeshould not be applied. No parity issues found; recommendparity-approved`.

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PratikDhanave (PratikDhanave) requested a review from a team as a code owner August 28, 2026 08:41

Copilot AI lite review requested due to automatic review settings August 28, 2026 08:41

Copilot started reviewing on behalf of PratikDhanave (PratikDhanave) August 28, 2026 08:41 View session

github-actions Bot added area:provider Changes files in the provider area area:provider/anthropic Changes files in the provider / anthropic area size:medium At most 100 changed lines across at most 5 files pending-auto-risk Automatic risk classification is in progress labels Aug 28, 2026

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github-actions Bot added parity-approved Go API consistency review found no parity issues risk:medium Contained production impact requiring normal review depth and removed pending-auto-risk Automatic risk classification is in progress labels Aug 28, 2026

Quim Muntal (qmuntal) requested changes Aug 31, 2026

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PratikDhanave (PratikDhanave) added 2 commits September 6, 2026 08:54

Merge remote-tracking branch 'upstream/main' into HEAD

a1aefde

github-actions Bot added pending-auto-risk Automatic risk classification is in progress and removed risk:medium Contained production impact requiring normal review depth labels Sep 6, 2026

github-actions Bot added risk:low Limited blast radius and straightforward rollback and removed pending-auto-risk Automatic risk classification is in progress labels Sep 6, 2026

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Forward a data: URIContent to Anthropic as an inline base64 block - #939

Forward a data: URIContent to Anthropic as an inline base64 block#939
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PratikDhanave (PratikDhanave) commented Aug 28, 2026

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