fix(s3-presigned-post): use starts-with condition for fields containing ${filename}#7771
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…ng ${filename}
When a field value (e.g. success_action_redirect) contains the
${filename} variable, S3 substitutes it with the actual uploaded
filename at upload time. The SDK was generating an exact-match
policy condition for these fields, which caused a policy mismatch
and AccessDenied error because the substituted value no longer
matched the literal ${filename} string.
This extends the existing ${filename} handling (which already
worked for the Key field) to all user-provided Fields. Any field
value containing ${filename} now gets a starts-with condition
instead of an exact match, allowing S3's variable substitution
to work correctly.
Fixes aws#7191
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Fixes #7191
Problem
When using
createPresignedPost()with${filename}in a field value (e.g.success_action_redirect), S3 rejects the upload withAccessDenied.S3 supports
${filename}variable substitution in POST uploads — at upload time, S3 replaces${filename}with the actual uploaded filename. However, the SDK generates an exact-match policy condition for all fields:{"success_action_redirect": "https://example.com/success?file=${filename}"}When S3 substitutes
${filename}with the real filename (e.g.test.txt), the field value becomeshttps://example.com/success?file=test.txt, which no longer matches the exact condition, causing a policy violation.The SDK already handles this correctly for the
Keyfield (line 82), but not for other fields.Solution
Extend the existing
${filename}detection to all user-providedFields. When a field value contains${filename}, generate astarts-withcondition instead of an exact match:This allows S3 to substitute
${filename}freely while still enforcing that the field value starts with the expected prefix.Changes
packages/s3-presigned-post/src/createPresignedPost.ts— check field values for${filename}and emitstarts-withconditionspackages/s3-presigned-post/src/createPresignedPost.spec.ts— add test for${filename}in field valuesBy submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.