Try #262:

src/AWSS3.jl

@@ -217,6 +217,9 @@ end
 [HEAD Object](http://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectHEAD.html)
 
 Retrieves metadata from an object without returning the object itself.
+
+!!! warning
+    This function returns the headers from `S3.head_object` as `Dict` of key-value pairs. [HTTP/1.1 headers are case insensitive](https://datatracker.ietf.org/doc/html/rfc2616#section-4.2) while [HTTP/2 headers must be lowercase](https://datatracker.ietf.org/doc/html/rfc7540#section-8.1.2). Therefore, the casing of the keys of the returned dict may depend on the HTTP client implementation (e.g. via `AWS.DownloadsBackend` vs `AWS.HTTPBackend`).
 """
 function s3_get_meta(
     aws::AbstractAWSConfig, bucket, path; version::AbstractS3Version=nothing, kwargs...

test/awss3.jl

@@ -98,12 +98,12 @@ function awss3_tests(config)
 
     @testset "Check Metadata" begin
         meta = s3_get_meta(config, bucket_name, "key1")
-        @test meta["ETag"] == "\"68bc8898af64159b72f349b391a7ae35\""
+        @test get_robust_case(meta, "ETag") == "\"68bc8898af64159b72f349b391a7ae35\""
     end
 
     @testset "default Content-Type" begin
         # https://github.com/samoconnor/AWSS3.jl/issues/24
-        ctype(key) = s3_get_meta(bucket_name, key)["Content-Type"]
+        ctype(key) = AWSS3.get_robust_case(s3_get_meta(bucket_name, key), "Content-Type")
 
         for k in ["file.foo", "file", "file_html", "file.d/html", "foobar.html/file.htm"]
             is_aws(config) && k == "file" && continue

test/runtests.jl

@@ -51,8 +51,17 @@ include("awss3.jl") # creates `s3path_tests(config)`
 
     # Set `AWSConfig` as the default for the following tests
     aws = global_aws_config(AWSConfig())
-    @testset "S3" begin
-        awss3_tests(aws)
-        s3path_tests(aws)
+
+    prev_backend = AWS.DEFAULT_BACKEND[]
+    for backend in (AWS.HTTPBackend, AWS.DownloadsBackend)
+        AWS.DEFAULT_BACKEND[] = backend()
+        try
+            @testset "S3 with $backend" begin
+                awss3_tests(aws)
+                s3path_tests(aws)
+            end
+        finally
+            AWS.DEFAULT_BACKEND[] = prev_backend
+        end
     end
 end

test/s3path.jl

@@ -631,6 +631,7 @@ function s3path_tests(config)
             alt_region = prev_config.region == "us-east-2" ? "us-east-1" : "us-east-2"
             try
                 global_aws_config(; region=alt_region) # this is the wrong region!
+                read(path, String)
                 @test_throws AWS.AWSException read(path, String)
 
                 # restore the right region