```
$ planemo --version
planemo, version 0.38.0.dev0
```

```
$ planemo shed_update --shed_target testtoolshed packages/package_mira_4_0_2/
cd '/mnt/shared/users/pc40583/repositories/pico_galaxy/packages/package_mira_4_0_2' && git rev-parse HEAD
cd '/mnt/shared/users/pc40583/repositories/pico_galaxy/packages/package_mira_4_0_2' && git diff --quiet
Could not update package_mira_4_0_2
Unexpected HTTP status code: 400: {"content_alert": "", "err_msg": "No changes to repository."}
Repository metadata updated successfully for repository package_mira_4_0_2.
Failed to update a repository.
```

Now using ``--check_diff``,

```
$ planemo shed_update --check_diff --shed_target testtoolshed packages/package_mira_4_0_2/
cd '/mnt/shared/users/pc40583/repositories/pico_galaxy/packages/package_mira_4_0_2' && git rev-parse HEAD
cd '/mnt/shared/users/pc40583/repositories/pico_galaxy/packages/package_mira_4_0_2' && git diff --quiet
Diffing repository [package_mira_4_0_2]
wget -q -O - 'https://testtoolshed.g2.bx.psu.edu/repository/download?repository_id=6777f9675c9051d3&changeset_revision=default&file_type=gz' | tar -xzf - -C /tmp/tool_shed_diff_YeKVAJ/_testtoolshed_ --strip-components 1

gzip: stdin: invalid compressed data--format violated
tar: Child returned status 1
tar: Error is not recoverable: exiting now
mkdir "/tmp/tool_shed_diff_YeKVAJ/_workingdir_"; tar -xzf "/tmp/tmpfuXDVs" -C "/tmp/tool_shed_diff_YeKVAJ/_workingdir_"; rm -rf /tmp/tmpfuXDVs
cd "/tmp/tool_shed_diff_YeKVAJ"; diff -r _workingdir_ _testtoolshed_
Repository [package_mira_4_0_2] not different, skipping upload.
Repository metadata updated successfully for repository package_mira_4_0_2.
```

What is this message and is it hiding a problem? It turns out to be something on the (Test) Tool Shed side:

```
$ wget -q -O - 'https://testtoolshed.g2.bx.psu.edu/repository/download?repository_id=6777f9675c9051d3&changeset_revision=default&file_type=gz' | head
UX?




body { color: #303030; background: #dfe5f9; font-family:"Lucida Grande",verdana,arial,helvetica,sans-serif; font-size:12px; line-height:16px; }
.content { max-width: 720px; margin: auto; margin-top: 50px; }

Internal Server Error
```

Verbose mode (e.g. with curl) shows the initial URL returns a 302 redirection, which ultimately gives an error message but not an error status:

```
$ curl -v 'https://testtoolshed.g2.bx.psu.edu/repos/peterjc/package_mira_4_0_2/archive/default.tar.gz'
* About to connect() to testtoolshed.g2.bx.psu.edu port 443 (#0)
* Trying 128.118.250.5... connected
* Connected to testtoolshed.g2.bx.psu.edu (128.118.250.5) port 443 (#0)
* Initializing NSS with certpath: sql:/etc/pki/nssdb
* CAfile: /etc/pki/tls/certs/ca-bundle.crt
CApath: none
* SSL connection using TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
* Server certificate:
* subject: CN=radegast.galaxyproject.org,OU=Center for Comparative Genomics and Bioinformatics,O=The Pennsylvania State University,L=University Park,ST=PA,postalCode=16802,C=US
* start date: Nov 11 00:00:00 2016 GMT
* expire date: Nov 11 23:59:59 2017 GMT
* common name: radegast.galaxyproject.org
* issuer: CN=InCommon RSA Server CA,OU=InCommon,O=Internet2,L=Ann Arbor,ST=MI,C=US
> GET /repos/peterjc/package_mira_4_0_2/archive/default.tar.gz HTTP/1.1
> User-Agent: curl/7.19.7 (x86_64-redhat-linux-gnu) libcurl/7.19.7 NSS/3.21 Basic ECC zlib/1.2.3 libidn/1.18 libssh2/1.4.2
> Host: testtoolshed.g2.bx.psu.edu
> Accept: */*
>
< HTTP/1.1 200 Script output follows
< Server: nginx/1.6.2
< Date: Wed, 01 Feb 2017 17:49:32 GMT
< Content-Type: application/x-gzip
< Transfer-Encoding: chunked
< Connection: keep-alive
< ETag: 1485971064
< Content-Disposition: attachment; filename=package_mira_4_0_2-default.tar.gz
<
UX?




body { color: #303030; background: #dfe5f9; font-family:"Lucida Grande",verdana,arial,helvetica,sans-serif; font-size:12px; line-height:16px; }
.content { max-width: 720px; margin: auto; margin-top: 50px; }

Internal Server Error

* Connection #0 to host testtoolshed.g2.bx.psu.edu left intact
* Closing connection #0
```

Reproduce the report with `planemo shed_update --check_diff --shed_target testtoolshed packages/package_mira_4_0_2/` and inspect the `shed_update --check_diff` entry point that downloads and extracts the Tool Shed archive. Determine how an HTTP error page returned with a success status is handled; done means the command reports the remote failure clearly without misleading gzip or diff output.

Written by the indexing model from the issue text.