Accommodate non-Amazon data center info metadata #44
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
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@@ -5,6 +5,7 @@ package fargo | |
| import ( | ||
| "encoding/json" | ||
| "encoding/xml" | ||
| "io" | ||
| "strconv" | ||
| ) | ||
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@@ -122,17 +123,22 @@ func (i *InstanceMetadata) MarshalJSON() ([]byte, error) { | |
| return i.Raw, nil | ||
| } | ||
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| // startLocalName creates a start-tag of an XML element with the given local name and no namespace name. | ||
| func startLocalName(local string) xml.StartElement { | ||
| return xml.StartElement{Name: xml.Name{Space: "", Local: local}} | ||
| } | ||
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| // MarshalXML is a custom XML marshaler for InstanceMetadata. | ||
| func (i InstanceMetadata) MarshalXML(e *xml.Encoder, start xml.StartElement) error { | ||
| tokens := []xml.Token{start} | ||
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| if i.parsed != nil { | ||
| for key, value := range i.parsed { | ||
| t := startLocalName(key) | ||
| tokens = append(tokens, t, xml.CharData(value.(string)), xml.EndElement{Name: t.Name}) | ||
| } | ||
| } | ||
| tokens = append(tokens, xml.EndElement{Name: start.Name}) | ||
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| for _, t := range tokens { | ||
| err := e.EncodeToken(t) | ||
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@@ -144,3 +150,152 @@ func (i InstanceMetadata) MarshalXML(e *xml.Encoder, start xml.StartElement) err | |
| // flush to ensure tokens are written | ||
| return e.Flush() | ||
| } | ||
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| type metadataMap map[string]string | ||
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| // MarshalXML is a custom XML marshaler for metadataMap, mapping each metadata name/value pair to a | ||
| // correspondingly named XML element with the pair's value as character data content. | ||
| func (m metadataMap) MarshalXML(e *xml.Encoder, start xml.StartElement) error { | ||
| if err := e.EncodeToken(start); err != nil { | ||
| return err | ||
| } | ||
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| for k, v := range m { | ||
| if err := e.EncodeElement(v, startLocalName(k)); err != nil { | ||
| return err | ||
| } | ||
| } | ||
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| return e.EncodeToken(start.End()) | ||
| } | ||
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| // UnmarshalXML is a custom XML unmarshaler for metadataMap, mapping each XML element's name and | ||
| // character data content to a corresponding metadata name/value pair. | ||
| func (m metadataMap) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error { | ||
| var v string | ||
| for { | ||
| t, err := d.Token() | ||
| if err != nil { | ||
| if err == io.EOF { | ||
| break | ||
| } | ||
| return err | ||
| } | ||
| if k, ok := t.(xml.StartElement); ok { | ||
| if err := d.DecodeElement(&v, &k); err != nil { | ||
| return err | ||
| } | ||
| m[k.Name.Local] = v | ||
| } | ||
| } | ||
| return nil | ||
| } | ||
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| func metadataValue(i DataCenterInfo) interface{} { | ||
| if i.Name == Amazon { | ||
| return i.Metadata | ||
| } | ||
| return metadataMap(i.AlternateMetadata) | ||
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There was a problem hiding this comment. Should this be named There was a problem hiding this comment. My use of "alternate" here is apparently a North American meaning, which is nearly synonymous with "alternative". I did some reading, and found this explanation ("Alternate' in American English):
Another source has this to say:
Here, our first choice is to use Amazon-related metadata. Failing that, we fall back to using the alternate metadata. To my ear, "alternative" makes it sound like we could choose either of them, but they should never both be available or used at the same time. It sounds like my choice might confuse our readers in UK, but their preferred form sounds strange to my North American ear. What to do? There was a problem hiding this comment. Giving that we use either one or another and not both at a time, I'm happy with |
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| } | ||
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| var ( | ||
| startName = startLocalName("name") | ||
| startMetadata = startLocalName("metadata") | ||
| ) | ||
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| // MarshalXML is a custom XML marshaler for DataCenterInfo, writing either Metadata or AlternateMetadata | ||
| // depending on the type of data center indicated by the Name. | ||
| func (i DataCenterInfo) MarshalXML(e *xml.Encoder, start xml.StartElement) error { | ||
| if err := e.EncodeToken(start); err != nil { | ||
| return err | ||
| } | ||
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| if err := e.EncodeElement(i.Name, startName); err != nil { | ||
| return err | ||
| } | ||
| if err := e.EncodeElement(metadataValue(i), startMetadata); err != nil { | ||
| return err | ||
| } | ||
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| return e.EncodeToken(start.End()) | ||
| } | ||
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| type preliminaryDataCenterInfo struct { | ||
| Name string `xml:"name" json:"name"` | ||
| Metadata metadataMap `xml:"metadata" json:"metadata"` | ||
| } | ||
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| func bindValue(dst *string, src map[string]string, k string) bool { | ||
| if v, ok := src[k]; ok { | ||
| *dst = v | ||
| return true | ||
| } | ||
| return false | ||
| } | ||
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| func populateAmazonMetadata(dst *AmazonMetadataType, src map[string]string) { | ||
| bindValue(&dst.AmiLaunchIndex, src, "ami-launch-index") | ||
| bindValue(&dst.LocalHostname, src, "local-hostname") | ||
| bindValue(&dst.AvailabilityZone, src, "availability-zone") | ||
| bindValue(&dst.InstanceID, src, "instance-id") | ||
| bindValue(&dst.PublicIpv4, src, "public-ipv4") | ||
| bindValue(&dst.PublicHostname, src, "public-hostname") | ||
| bindValue(&dst.AmiManifestPath, src, "ami-manifest-path") | ||
| bindValue(&dst.LocalIpv4, src, "local-ipv4") | ||
| bindValue(&dst.HostName, src, "hostname") | ||
| bindValue(&dst.AmiID, src, "ami-id") | ||
| bindValue(&dst.InstanceType, src, "instance-type") | ||
| } | ||
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| func adaptDataCenterInfo(dst *DataCenterInfo, src preliminaryDataCenterInfo) { | ||
| dst.Name = src.Name | ||
| if src.Name == Amazon { | ||
| populateAmazonMetadata(&dst.Metadata, src.Metadata) | ||
| } else { | ||
| dst.AlternateMetadata = src.Metadata | ||
| } | ||
| } | ||
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| // UnmarshalXML is a custom XML unmarshaler for DataCenterInfo, populating either Metadata or AlternateMetadata | ||
| // depending on the type of data center indicated by the Name. | ||
| func (i *DataCenterInfo) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error { | ||
| p := preliminaryDataCenterInfo{ | ||
| Metadata: make(map[string]string, 11), | ||
| } | ||
| if err := d.DecodeElement(&p, &start); err != nil { | ||
| return err | ||
| } | ||
| adaptDataCenterInfo(i, p) | ||
| return nil | ||
| } | ||
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| // MarshalJSON is a custom JSON marshaler for DataCenterInfo, writing either Metadata or AlternateMetadata | ||
| // depending on the type of data center indicated by the Name. | ||
| func (i DataCenterInfo) MarshalJSON() ([]byte, error) { | ||
| type named struct { | ||
| Name string `json:"name"` | ||
| } | ||
| if i.Name == Amazon { | ||
| return json.Marshal(struct { | ||
| named | ||
| Metadata AmazonMetadataType `json:"metadata"` | ||
| }{named{i.Name}, i.Metadata}) | ||
| } | ||
| return json.Marshal(struct { | ||
| named | ||
| Metadata map[string]string `json:"metadata"` | ||
| }{named{i.Name}, i.AlternateMetadata}) | ||
| } | ||
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| // UnmarshalJSON is a custom JSON unmarshaler for DataCenterInfo, populating either Metadata or AlternateMetadata | ||
| // depending on the type of data center indicated by the Name. | ||
| func (i *DataCenterInfo) UnmarshalJSON(b []byte) error { | ||
| p := preliminaryDataCenterInfo{ | ||
| Metadata: make(map[string]string, 11), | ||
| } | ||
| if err := json.Unmarshal(b, &p); err != nil { | ||
| return err | ||
| } | ||
| adaptDataCenterInfo(i, p) | ||
| return nil | ||
| } | ||
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Should we call
Flush()here?https://golang.org/pkg/encoding/xml/#Encoder.EncodeToken
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The documentation mentions creating an
Encoder:Here, I didn't create the
Encoder; it's created implicitly over infargo.marshalin file net.go. Note thatxml.Marshalcreates anEncoderand callsEncodeon it, which in turn flushes when it's done writing. Hence I don't think that callingFlushexplicitly here is necessary.