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Handling Redirects, 6. Using Range Headers

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Most of these client libraries will take care of the low-level protocol issues for you. Formatting the requests and interpreting the responses are usually much easier with an existing framework. In fact, much of the SCSP discussion above can be skipped, allowing the framework to do the work for you. 3.5. Handling Redirects Some HTTP client libraries and frameworks do not handle redirects correctly for WRITE requests, at least not by default. Older versions of the HTTP protocol, namely HTTP/1.0, were lax in their specification of exactly what the client must do when it receives a 301 or a 307 response code. Because of this, older clients, including many web browsers, developed their own conventions. While some of these conventions might be useful, they are in direct violation of the HTTP/1.1 specification and therefore incompatible with DX Storage. Both the Microsoft .NET framework and the libCURL framework (and probably others) are known to process a redirect from a POST request by changing the POST to a GET and then sending the new request to the redirect server. Workarounds exist in the impacted frameworks because the behavior is known to be in violation of the specification. To quote RFC 2616: "When automatically redirecting a POST request after receiving a 301 status code, some existing HTTP/1.0 user agents will erroneously change it into a GET request." 3.6. Using Range Headers In some cases, an application might be interested in only a byte portion of a larger object stored in DX Storage. Rather than read the entire object and filter out the interesting parts, the application can include one or more Range headers with an SCSP READ request. A READ request can include more than one Range header. Consult the HTTP/1.1 specification for a thorough discussion of Range headers. Here are some examples and their interpretations: Range: 0-499 Return the first 500 bytes of the object Range: 500-999 Return the second 500 bytes Range: -500 Return the last 500 bytes Range: 0-499, 500-999 Return the first 1000 bytes Note Range headers are not compatible with integrity seals because an integrity seal is a hash of the object's entire contents. If the Range is not set to a value greater than or equal to the size of the object, the connection is closed as if the integrity seal was invalid. For more information about integrity seals, see Section 20.1, "Integrity Seals". READ requests that include invalid Range headers (for example, ranges that do not exist in the object) cause DX Storage to respond with a 416 Range not satisfiable error. A successful response to a READ that includes one or more Range headers is 206 Partial content. Of course, only data in the requested ranges are included in the 206 response. READ requests that include a range like Range: 0-199, 300-349, 500-999 returns a Content-Type: multipart/byteranges response consisting of three parts: 200, 50, and 500 bytes of content. For more information, see section 14.35 (Range) and appendix 19.2 (Internet Media Type multipart/ byteranges) in the HTTP/1.1 RFC. Copyright © 2010 Caringo, Inc. All rights reserved 13 Version 5.0 December 2010

Section	Page
DX Object Storage Application Guide	1
Table of Contents	3
Chapter 1. Introduction to DX Storage Objects	6
1.1. Introducing Named Objects	6
1.2. Summary of Named Objects and Unnamed Objects	7
1.3. Common Named Object Terminology	7
1.4. About DX Storage Object Types	8
1.5. Bucket and Object Naming Rules	8
1.6. Simple Examples of Creating Buckets and Named Objects	8
1.7. Universal Resource Identifiers (URIs)	9
1.8. About Objects and Security	10
1.8.1. The Basics of DX Storage Security	10
1.8.2. Commonly Used Security Terminology	11
1.8.3. Basic Security Guidelines	11
1.9. Concepts for Unnamed Objects	11
1.9.1. Universally Unique Identifiers (UUIDs)	11
1.9.2. About Immutable Objects	12
1.9.3. About Anchor Streams	12
1.10. Document Typographical Conventions	13
Chapter 2. Connecting to a DX Storage Cluster	14
2.1. About the Primary Access Node (PAN)	14
2.2. Requirements for Node Accessibility	14
2.2.1. Using the DX Storage Software Development Kit (SDK)	14
2.2.2. Using Multicast-DNS (mDNS)	15
2.2.3. Using DNS Round Robin	15
2.2.4. Using a Pool of Static IP Addresses	16
2.2.5. Using a Single Static IP Address	16
Chapter 3. Application Best Practices	17
3.1. Using the Software Development Kit (SDK)	17
3.2. Dynamically Locating DX Storage Nodes	17
3.3. Optimizing Bucket and Domain Operations	17
3.4. Using HTTP Client Libraries	17
3.5. Handling Redirects	18
3.6. Using Range Headers	18
3.7. Multi-Threading	19
3.8. Using Persistent Connections	19
Chapter 4. Introduction to the Simple Content Storage Protocol (SCSP)	20
4.1. Mapping SCSP Operations to HTTP Methods	20
4.2. HTTP Overview	21
4.3. Requests and Responses	21
4.3.1. HTTP Response Codes	21
4.3.2. Redirect Responses	22
4.4. Formatting SCSP Commands for Named and Unnamed Objects	22
4.5. Undefined Responses from DX Storage	23
4.6. Normal Response Headers	24
Chapter 5. SCSP READ	27
5.1. Introduction to READ	27
5.1.1. Reading With Content Validation	27
5.1.2. Requestion Node Status and Cluster Capacity	27
5.2. Unnamed Object READ Details	28
5.3. Normal Responses to READ	28
5.3.1. Normal READ Responses for Named Objects	28
5.3.1.1. Normal READ Response for a Domain	28
5.3.1.2. Normal READ Response for a Bucket	29
5.3.1.3. Normal READ Response for a Named Object	29
5.3.2. Normal READ Response for Unnamed Objects	29
5.3.3. Other Normal READ Responses	30
5.4. Error Responses to READ	30
Chapter 6. SCSP WRITE	32
6.1. Introduction to WRITE	32
6.1.1. About the Expect: 100-continue Header and WRITE	33
6.1.2. About Replicate On Write	33
6.2. Named Object WRITE Details	33
6.3. Unnamed Object WRITE Details	33
6.4. Normal Responses to WRITE	33
6.5. Error Responses to WRITE	34
Chapter 7. SCSP DELETE	36
7.1. Introduction to DELETE	36
7.2. Unnamed Object DELETE Details	37
7.3. Named Object DELETE Details	37
7.4. Normal Responses to DELETE	37
7.5. Error Responses to DELETE	38
Chapter 8. SCSP UPDATE	39
8.1. Introduction to UPDATE	39
8.2. Unnamed Object UPDATE Details	39
8.3. Normal Responses to UPDATE	40
Chapter 9. SCSP COPY	41
9.1. Introduction to COPY	41
9.2. Unnamed Object COPY Details	41
9.3. Normal Responses to COPY	41
Chapter 10. SCSP APPEND	42
10.1. Introduction to APPEND	42
10.2. Unnamed Object APPEND Details	43
10.3. Normal Responses to APPEND	43
Chapter 11. SCSP INFO	44
11.1. Introduction to INFO	44
11.1.1. Getting Replica Counts	44
11.1.2. Getting Node Status and Cluster Capacity	44
11.2. Unnamed Object INFO Details	45
11.3. Normal Responses to INFO	45
11.3.1. Normal INFO Responses for Named and Unnamed Objects	45
11.3.2. Normal INFO Responses for Named Objects	46
11.3.3. Normal INFO Responses for Unnamed Objects	47
11.4. Error Responses to INFO	47
Chapter 12. Introduction to Object Security	48
12.1. About Security Roles	48
12.2. Security Realm Overview	49
12.2.1. Common Security Terminology	49
12.2.2. About Security Realms	49
12.2.3. About Realm Caching and Security	49
12.3. About Authorization Header Syntax	50
12.3.1. About Realm Names	51
12.3.1.1. About Realms and Buckets	51
12.3.1.2. About owner@ and @owner Syntax	51
12.3.1.3. About user@realm Syntax	51
12.4. Authorization Specification Examples	51
12.5. About Authorization Header Evaluation	52
12.6. Creating Realms	53
12.7. Updating the Realm on a Bucket	54
12.8. Administrative Override and Security	54
Chapter 13. Managing Security for Application Developers	55
13.1. What Application Developers Need to Know	55
13.2. About Bucket Authorization	55
13.3. Example: Creating Bucket Owners	56
13.4. Examples of Creating Buckets and Named Objects	56
Chapter 14. Managing Security for Domain Managers	59
14.1. What Domain Managers Need to Know	59
14.2. About Domain Manager Tasks and Responsibilities	59
14.3. Examples of Updating Domain and Administrator User Lists	59
14.3.1. Updating the Domain Realm	60
14.3.2. Updating the Domain Manager Realm	61
14.3.3. Updating a Realm Using PUT	62
Chapter 15. Using the Content-MD5 Metadata Header	64
Chapter 16. Using Lifepoint Metadata Headers	65
16.1. About Storage Policies	65
16.2. A Simple Lifecycle Example	65
16.3. Lifepoint/Lifecycle Specification	66
16.4. Constraint Types	66
16.4.1. Replication	67
16.4.2. Deletion	67
Chapter 17. Using the Allow Metadata Header	69
17.1. Overview of the Allow Header	69
17.2. Administrative Override	69
Chapter 18. Using Caching Metadata Headers	71
18.1. About Caching Headers	71
18.2. Using HTTP/1.0 Caching Headers	71
18.2.1. Last-Modified	71
18.2.2. If-Modified-Since	71
18.2.3. If-Unmodified-Since	71
18.2.4. Expires	72
18.3. Using HTTP/1.1 Caching Headers	72
18.3.1. ETag	72
18.3.2. If-Match	72
18.3.3. If-None-Match	73
18.3.4. If-Range	73
Chapter 19. Using Custom Metadata Headers	75
Chapter 20. Basic Content Integrity Assurance	76
20.1. Integrity Seals	76
20.2. Validating Reads	76
20.3. Application Initiated Hash Upgrading	77
Appendix A. Content Header Metadata	78
Appendix B. Sample Code and Client Library Behaviors with 100-Continue	80

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Version 5.0

December 2010

Most of these client libraries will take care of the low-level protocol issues for you. Formatting the

requests and interpreting the responses are usually much easier with an existing framework. In fact,

much of the SCSP discussion above can be skipped, allowing the framework to do the work for you.

3.5. Handling Redirects

Some HTTP client libraries and frameworks do not handle redirects correctly for WRITE requests,

at least not by default. Older versions of the HTTP protocol, namely HTTP/1.0, were lax in their

specification of exactly what the client must do when it receives a 301 or a 307 response code.

Because of this, older clients, including many web browsers, developed their own conventions.

While some of these conventions might be useful, they are in direct violation of the HTTP/1.1

specification and therefore incompatible with DX Storage.

Both the Microsoft .NET framework and the libCURL framework (and probably others) are known to

process a redirect from a POST request by changing the POST to a GET and then sending the new

request to the redirect server. Workarounds exist in the impacted frameworks because the behavior

is known to be in violation of the specification. To quote

RFC 2616

"When automatically redirecting a POST request after receiving a 301 status code, some existing

HTTP/1.0 user agents will erroneously change it into a GET request."

3.6. Using Range Headers

In some cases, an application might be interested in only a byte portion of a larger object stored in

DX Storage. Rather than read the entire object and filter out the interesting parts, the application

can include one or more

Range headers

with an SCSP READ request. A READ request can include

more than one Range header. Consult the

HTTP/1.1 specification

for a thorough discussion of

Range headers. Here are some examples and their interpretations:

Range: 0-499

Return the first 500 bytes of the object

Range: 500-999

Return the second 500 bytes

Range: -500

Return the last 500 bytes

Range: 0-499, 500-999

Return the first 1000 bytes

Note

Range headers are not compatible with integrity seals because an integrity seal is a hash

of the object's entire contents. If the Range is not set to a value greater than or equal

to the size of the object, the connection is closed as if the integrity seal was invalid. For

more information about integrity seals, see

Section 20.1, “Integrity Seals”

READ requests that include invalid Range headers (for example, ranges that do not exist in the

object) cause DX Storage to respond with a

416 Range not satisfiable

error. A successful response

to a READ that includes one or more Range headers is

206 Partial content

. Of course, only data in

the requested ranges are included in the 206 response.

READ requests that include a range like

Range: 0-199, 300-349, 500-999

returns a

Content-Type: multipart/byteranges

response consisting of three parts: 200, 50, and 500

bytes of content.

For more information, see

section 14.35 (Range)

and

appendix 19.2 (Internet Media Type multipart/

byteranges)

in the

HTTP/1.1 RFC