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This section provides general information about SCSP WRITE that applies to both named and unnamed objects.
WRITE is a request to the storage cluster to create a new object. The WRITE request is formatted as a simple HTTP request using the POST method.
SCSP Method | HTTP Method | RFC 7231 Section |
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SCSP WRITE | POST |
| Info | |
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| title | Write for contextsThe Swarm setting scsp.requireExplicitContextCreate protects content-bearing objects from being created erroneously as contexts (buckets or domains). With this setting enabled, Swarm will not create a context object unless it includes the required header: Content-type: application/castorcontext. (v9.1) |
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| title | S3 compatibilityThe Swarm setting scsp.autoContentMD5Computation improves S3 compatibility by automating Content-MD5 hashing, which means that you do not need to include the gencontentmd5 query argument or the deprecated Expect: Content-MD5 header on writes (although you may want to supply your own Content-MD5 header for content integrity checking). This setting is ignored wherever it is invalid, such as on a multipart initiate/complete or an EC APPEND. (v9.1) |
WRITE for named objects
If you WRITE a named object that already exists, the existing object is overwritten with a new version.
WRITE that overwrites object
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POST /bucket/photo.jpg HTTP/1.1 Host: cluster.example.com User-Agent: Swarm Client/0.1 Content-Length: 43402 Expect: 100-continue Content-Type: image/jpeg Content-Language: en/us, x-pig-latin Content-Version: 42 CRLF [ content ] |
To prevent overwriting an existing object, include the If-None-Match: * request header.
If the named object does not exist, Swarm WRITEs the named object.
If the named object exists, Swarm responds with a 412 Precondition Fail error.
WRITE that prevents overwriting
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POST /bucket/photo.jpg HTTP/1.1 If-None-Match: * Host: cluster.example.com User-Agent: Swarm Client/0.1 Content-Length: 43402 Expect: 100-continue Content-Type: image/jpeg Content-Language: en/us, x-pig-latin Content-Version: 42 CRLF [ content ] |
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If you want to configure Swarm to allow you to use the HTTP PUT operation to create new named objects, add the scsp.allowPutCreate=True to your configuration parameters. You can also enable it using the putcreate query argument.
| Info | |
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| title | ExceptionAlthough domains and buckets are named, Swarm processes all PUT requests on these objects as updates, regardless of the setting.
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Preventing overwriting: If-None-Match
In contrast to an unnamed object, if you WRITE a named object that already exists, the existing object is overwritten with a new version. To prevent overwriting an existing object, include the If-None-Match: * request header.
If the named object does not exist, Swarm WRITEs the named object.
If the named object exists, Swarm responds with a 412 Precondition Fail error.
| Info |
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NoteSwarm returns a 412 error on SCSP WRITE of named objects if the domain or bucket does not exist or cannot be loaded. |
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NoteIf‑None‑Match:* can erroneously report that an object exists during the time window after it is flagged for deletion by policy but before it is removed from disk. This window is determined by the HP cycle time. |
WRITE for unnamed objects
Swarm makes no assumptions about User-Agent (except that it is an HTTP/1.1 client). The Host header must conform to the requirements of Section 14.23 of the HTTP/1.1 spec.
WRITE unnamed to host domain
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POST / HTTP/1.1 Host: cluster.example.com User-Agent:Swarm Client/0.1 Content-Length: 43402 Expect: 100-continue Content-Type: image/jpeg Content-Language: en/us, x-pig-latin Content-Version: 42 CRLF [ content ] |
If you WRITE an unnamed object, a new object is created and a new UUID is returned. If you WRITE an alias object, a new object is created and a new alias UUID is returned.
See WRITE for Unnamed Objects.
WRITE for alias objects
To create alias objects, add alias=yes:
WRITE for alias object
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POST /?alias HTTP/1.1 Host: cluster.example.com User-Agent: Swarm Client/0.1 |
WRITE for erasure-coded objects
A new object written to the storage cluster is erasure-coded if it meets the EC criteria language.
See Working with Large Objects.
| Info | |
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| title | NoteIf you WRITE an object of more than 4 TB in size, Swarm returns a 503 Service Unavailable error. |
WRITE for large files (Expect: 100-continue)
The Expect: 100-continue header tells the server that the client will wait after sending the header lines and before sending the content in the message body. The Swarm server can respond with a redirect or an error response.
If the server is ready to store the contents, it returns a 100 Continue response, telling the client to transmit the entity body. The client should wait for a 100 Continue response from the server before proceeding to send the data.
If the server is not ready, it sends a 413 Request entity too large error response and closes the connection.
Swarm allows the client to omit the Expect: 100-continue header, sending all the content at once. In response, the server reads and discards all data if it must respond with a redirect or error. For WRITE messages that include more than 65536 bytes, Swarm logs a warning:
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Error if Expect header is missing
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Please use Expect: 100-continue for large amounts of data. |
If any node in the cluster does not have enough space to write the object, the cluster returns a 507 Insufficient Storage error.
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