data-source/aws_iam_policy_document: Prevent panic when combining single principal identifier with multiple principal identifiers

[bflad]

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Closes #10777

Release note for CHANGELOG:

* data-source/aws_iam_policy_document: Prevent panic when combining single principal identifier with multiple principal identifiers

Output from acceptance testing before fix:

=== CONT  TestAccAWSDataSourceIAMPolicyDocument_Statement_Principal_Identifiers_StringAndSlice
panic: interface conversion: interface {} is string, not []string [recovered]
  panic: interface conversion: interface {} is string, not []string

goroutine 254 [running]:
encoding/json.(*encodeState).marshal.func1(0xc00158f5a8)
  /usr/local/Cellar/go/1.13.4/libexec/src/encoding/json/encode.go:305 +0x9a
panic(0x5a68a40, 0xc000d48210)
  /usr/local/Cellar/go/1.13.4/libexec/src/runtime/panic.go:679 +0x1b2
github.com/terraform-providers/terraform-provider-aws/aws.IAMPolicyStatementPrincipalSet.MarshalJSON(0xc000a17580, 0x2, 0x2, 0x100c733, 0x5a73f60, 0x591b720, 0x7178801, 0xbbd7098)
  /Users/bflad/src/github.com/terraform-providers/terraform-provider-aws/aws/iam_policy_model.go:101 +0x866

Output from acceptance testing after fix:

--- PASS: TestAccAWSDataSourceIAMPolicyDocument_Statement_Principal_Identifiers_StringAndSlice (10.23s)
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_noStatementMerge (10.26s)
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_basic (10.29s)
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_noStatementOverride (10.30s)
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_sourceConflicting (10.40s)
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_override (10.53s)
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_duplicateSid (11.02s)
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_Version_20081017 (14.87s)
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_source (15.20s)

[netproteus]

Can confirm this fixes the issue I opened as well as the more complex config which was crashing.

[netproteus]

@bflad unfortunately there is still something funny going on with multiple principals

data "aws_iam_policy_document" "some-policy" {
  statement {
    effect = "Allow"

    actions = [
      "*"
    ]

    resources = [
      "*",
    ]

    principals {
      identifiers = [
        "arn:aws:iam::111111111111:root",
        "arn:aws:iam::222222222222:root",
      ]
      type = "AWS"
    }
    principals {
      identifiers = [
        "arn:aws:iam::333333333333:root",
      ]
      type = "AWS"
    }
    principals {
      identifiers = [
        "arn:aws:iam::444444444444:root",
      ]
      type = "AWS"
    }
  }
}

output "some-policy-json" {
  value = data.aws_iam_policy_document.some-policy.json
}

yields the following

some-policy-json = {
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "",
      "Effect": "Allow",
      "Action": "*",
      "Resource": "*",
      "Principal": {
        "AWS": [
          "arn:aws:iam::444444444444:root",
          "arn:aws:iam::222222222222:root",
          "arn:aws:iam::111111111111:root"
        ]
      }
    }
  ]
}

[netproteus]

The following fix works for me but I'm not that proficient in go so please check it carefully

@@ -105,7 +106,17 @@ func (ps IAMPolicyStatementPrincipalSet) MarshalJSON() ([]byte, error) {
                        sort.Sort(sort.Reverse(sort.StringSlice(i)))
                        raw[p.Type] = append(raw[p.Type].([]string), i...)
                case string:
-                       raw[p.Type] = i
+                       switch v := raw[p.Type].(type) {
+                       case nil:
+                               raw[p.Type] = i
+                       case string:
+                               // Convert to []string to stop drop of principals
+                               raw[p.Type] = make([]string, 0, 2)
+                               raw[p.Type] = append(raw[p.Type].([]string), v)
+                               raw[p.Type] = append(raw[p.Type].([]string), i)
+                       case []string:
+                               raw[p.Type] = append(raw[p.Type].([]string), i)
+                       }
                default:
                        return []byte{}, fmt.Errorf("Unsupported data type %T for IAMPolicyStatementPrincipalSet", i)
                }

[netproteus]

Patch in previous comment is PR to this PR here with tests: #10844

[gdavison]

LGTM 👍

[ghost]

This has been released in version 2.37.0 of the Terraform AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template for triage. Thanks!

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!