Bug in unreleased code, introduced on master during 1.7 development. This bug does not affect released versions.

The driver correctly strips the "[" and "]" characters from the host in a URI like "mongodb://[::1]" before calling getaddrinfo on the host in mongoc_topology_scanner_node_connect_tcp(). In single-client mode, that is the only getaddrinfo call; the connection established by the topology scanner is also used for application operations.

In pooled mode, however, there is a second path for establishing connections for application operations, in mongoc_client_connect_tcp. This second path does not strip "[" and "]" from the hostname, and so it calls getaddrinfo on a misformatted string like "[::1]" instead of the intended "::1".

Connecting to "mongodb://[::1]" in pooled mode fails, therefore, with an error like "Failed to resolve [::1]".